THE  PRACTICAL  METHODS  OF 
ORGANIC  CHEMISTRY 


THE  MACMILLAN  COMPANY 

NEW  YORK    •    BOSTON   •    CHICAGO    •    DALLAS 
ATLANTA  •    SAN   FRANCISCO 

MACMILLAN  &  CO.,  LIMITED 

LONDON    •    BOMBAY    •    CALCUTTA 
MELBOURNE 

THE  MACMILLAN  CO.  OF  CANADA,  LTD, 

TORONTO 


THE  PRACTICAL  METHODS 


OF 

ORGANIC  CHEMISTRY 

BY 

LUDWIG   GATTERMANN,  PH.D. 

PROFESSOR    IN   THE   UNIVERSITY   OF   FREIBURG 

WITH  N UMER O  US  ILL  US TRA  TIONS 

TRANSLATED   BY 

WILLIAM    B.  SCHOBER,  PH.D. 

PROFESSOR   OF   CHEMISTRY   IN    LEHIGH    UNIVERSITY 
AND 

VAHAN    S.  BABASINIAN,  PH.D. 

ASSOCIATE   PROFESSOR   OF   ORGANIC   CHEMISTRY   IN    LEHIGH    UNIVERSITY 


A  UTHORISED    TRANSLA  TION 
THE  THIRD  AMERICAN  FROM  THE  ELEVENTH  GERMAN  EDITION 


THE    MACMILLAN    COMPANY 
1921 

*i? 

All  rights  reserved 
\ 


COPYRIGHT,  1896,  1901,  1914, 
BY  THE  MACMILLAN   COMPANY, 


J.  8.  Gushing  Co.  —  Berwick  &  Smith  Co. 
Norwood,  Mass.,  U.S.A. 


, 


TRANSLATOR'S   PREFACE 


'  THE  success  of  Professor  Gattermann's  book  in  the  original 
has  warranted  its  reproduction  in  English.  The  translation  is 
intended  for  those  students  of  chemistry  who  have  not  yet 
become  sufficiently  familiar  with  scientific  German  to  be  able 
to  read  it  accurately  without  constant  reference  to  a  dictionary. 
To  such  students  this  translation  is  offered,  in  the  hope  that  it 
will  increase  their  interest  in  the  science  without  causing  a  cor- 
responding decrease  in  their  efforts  to  acquire  a  knowledge  of 
German,  which  is  indispensable  to  every  well-trained  chemist. 

My  grateful  acknowledgments  are  due  to  my  colleague,  Dr. 
H.  M.  Ullmann,  for  many  valuable  suggestions,  and  to  Professor 
Gattermann  for  his  courtesy  in  pointing  out  several  inaccuracies 
in  the  German  edition. 

WILLIAM   B.   SCHOBER. 
SOUTH  BETHLEHEM,  PENNSYLVANIA, 
April,  1896. 


PREFACE 


THE  present  book  has  resulted  primarily  from  the  private  needs 
of  the  author.  If  one  is  obliged  to  initiate  a  large  number  of 
students  at  the  same  time  into  organic  laboratory  work,  it  is 
frequently  impossible,  even  with  the  best  intentions,  to  direct  the 
attention  of  each  individual  to  the  innumerable  details  of  labo- 
ratory methods.  In  order  that  students,  even  in  the  absence  of 
the  instructor,  can  gain  the  assistance  necessary  for  the  carrying 
out  of  the  common  operations,  a  General  Part,  dealing  with 
crystallisation,  distillation,  drying,  analytical  operations,  etc.,  is 
given  before  the  special  directions  for  Preparations.  In  the 
composition  of  this  General  Part,  it  has  been  considered  of 
more  value  to  describe  the  most  important  operations  in  such 
a  way  that  the  beginner  may  be  able  to  carry  out  the  directions 
independently,  rather  than  to  give  as  fully  as  possible  the  numer- 
ous modifications  of  individual  operations.  In  the  Special  Part, 
to  each  preparation  are  added  general  observations,  which  relate 
to  the  character  and  general  significance  of  the  reaction  carried 
out  in  practice ;  and  the  result  follows,  that  the  student  during 
the  period  given  to  laboratory  work,  becomes  familiar  with  the 
most  varied  theoretical  knowledge,  which,  acquired  under  these 
conditions  adheres  more  firmly,  as  is  well  known,  than  if  that 
knowledge  were  obtained  exclusively  from  a  purely  theoretical 

vii 


Vili  PREFACE 

book.  And  so  the  author  hopes  that  his  book,  along  with  the 
excellent  "  Introductions  "  of  E.  Fischer  and  Levy,  may  here  and 
there  win  some  friends. 

For  the   assistance   given  by  his  colleagues,  in  pointing  out 
deficiencies  of  his  work,  the  author  will  always  be  grateful. 

GATTERMANN. 

HEIDELBERG,  August,  1894, 


PREFACE   TO   THE   SECOND  AMERICAN 
EDITION 


IN  the  preparation  of  this  new  edition  advantage  has  been 
taken  of  the  opportunity  offered  to  correct  a  number  of  errors 
in  the  first  edition,  and  to  make  the  text  a  reproduction  of 
the  fourth  German  edition  of  Professor  Gattermann's  book.  In 
many  cases  the  laboratory  directions  have  been  improved,  a 
number  of  new  illustrations  have  been  added,  and  the  Special 
Part  now  includes  methods  for  the  preparation  of  glycol,  di- 
methylcyclohexenone,  s-xylenol,  phenylhydroxylamine,  nitroso- 
benzene,  p-tolyl  aldehyde  (Gattermann-Koch  synthesis),  salicylic 
aldehyde  (Reimer  and  Tiemann's  oxyaldehyde  synthesis),  cuprous 
chloride,  the  decomposition  of  inactive  mandelic  acid  into  its 
active  constituents,  and  a  zinc  dust  determination.  The  prepara- 
tions of  acetylene  and  acetylene  tetrabromide  have  been  omitted. 

WILLIAM   B.  SCHOBER. 

SOUTH  BETHLEHEM,  PENNSYLVANIA, 
May,  1901. 


PREFACE    TO    THE    THIRD    AMERICAN 
EDITION 

DURING  my  absence  from  the  University  on  sick  leave,  my 
colleague,  Professor  Vahan  S.  Babasinian,  has  undertaken  the 
entire  labor  and  responsibility,  —  including  the  translation,  edit- 
ing, and  reading  the  proofs,  —  involved  in  the  preparation  of  the 
new  edition  of  this  book.  To  him,  therefore,  is  due  all  the  credit 
for  the  satisfactory  results  presented  in  the  following  pages. 

WILLIAM    B.    SCHOBER. 


THIS  new  edition  is  a  reproduction  of  the  eleventh  German 
edition  of  Professor  Gattermann's  book.  A  number  of  errors  in 
the  second  edition  have  been  corrected,  four  new  illustrations 
have  been  added,  improved  methods  for  the  preparation  of  ethyl- 
ene,  glycol  and  carbon  monoxide  have  been  outlined,  Dennstedt's 
Method  of  Analysis  and  Grignard's  Reaction  have  been  fully  de- 
scribed. This  edition  contains  also  discussions  of  the  theoretical 
grounds  upon  which  rest  the  processes  of  distillation  with  steam, 
salting  out,  separation  by  extraction  and  esterification. 


VAHAN   S.    BABASINIAN. 


SOUTH  BETHLEHEM,  PENNSYLVANIA, 
September,  1913. 


CONTENTS 

GENERAL  PART 

PAGE 

Crystallisation I 

Sublimation    .         .         .         .         .         .         .         .         .         .         .         .14 

Distillation 16 

Distillation  with  Steam 37 

Separation  of  Liquid  Mixtures.     Separation  by  Extraction.     Salting  Out  43 

Decolourising.     Removal  of  Tarry  Matter       ......  50 

Drying 52 

Filtration 56 

Heating  under  Pressure 63 

Melting-point 71 

Drying  and  Cleaning  of  Vessels 75 

ORGANIC   ANALYTICAL   METHODS 

Detection  of  Carbon,  Hydrogen,  Nitrogen,  Sulphur,  and  the  Halogens  .  77 

Quantitative  Determination  of  the  Halogens.     Carius'  Method       .         .  80 

Quantitative  Determination  of  Sulphur.     Carius'  Method        ...  86 

Quantitative  Determination  of  Nitrogen.     Dumas'  Method    ...  9° 

Quantitative  Determination  of  Carbon  and  Hydrogen.    Liebig's  Method  101 

Elementary  Analysis.     Dennstedt's  Method   .         .         .         .         „         .  113 

SPECIAL  PART 

I.     ALIPHATIC   SERIES 

1.  Reaction:  The  Replacement  of  an  Alcoholic  Hydroxyl  Group  by  a 

Halogen I31 

2.  Reaction:  Preparation  of  an  Acid-Chloride  from  the  Acid         .         .  141 

3.  Reaction:   Preparation  of  an  Anhydride  from  the  Acid-Chloride  and 

the  Sodium  Salt  of  the  Acid H7 

xiii 


xiv  CONTENTS 

PAGB 

4.  Reaction :  Preparation  of  an  Acid-Amide  from  the  Ammonium  Salt 

of  the  Acid 151 

5.  Reaction:  Preparation  of  an  Acid-Nitrile  from  an  Acid- Amide        .     155 

6.  Reaction :   Preparation  of  an  Acid- Ester  from  the  Acid  and  Alcohol     157 

7.  Reaction:   Substitution  of  Hydrogen  by  Chlorine    .         .         .         .163 

8.  Reaction:  Oxidation  of  a  Primary  Alcohol  to  an  Aldehyde      .         .167 

9.  Reaction :   Preparation  of  a  Primary  Amine  from  an  Acid-Amide  of 

the  next  Higher  Series 175 

10.  Reaction :    Syntheses  of  Ketone  Acid-Esters  or  Polyketones  with 

Sodium  or  Sodium  Alcoholate .     179 

11.  Reaction:  Syntheses  of  the  Homologues  of  Acetic  Acid  by  means 

of  Malonic  Ester 185 

12.  Reaction:  Preparation  of  a  Hydrocarbon  of  the  Ethylene  Series  by 

the  Elimination  of  Water  from  an  Alcohol.     Union  with  Bromine     191 

13.  Reaction:   Replacement  of  Halogen  Atoms  by  Alcoholic  Hydroxyl 

Groups          ...........     196 

TRANSITION  FROM  THE  ALIPHATIC  TO  THE  AROMATIC 
SERIES 

Dimethylcyclohexenone  and  s-Xylenol  from  Ethylidenebisacetacetic  Ester 

(Ring  Closing  in  a  1.5  Diketone.     Knoevenagel  Reaction)          .     202 

II.     AROMATIC  SERIES 

1.  Reaction:  Nitration  of  a  Hydrocarbon 212 

2.  Reaction:   Reduction  of  a  Nitro-Compound  to  an  Amine         .         .     215 

3.  Reaction  :   (a)  Reduction  of  a  Nitro-Compound  to  a  Hydroxylamine 

Derivative.     (£)  Oxidation  of  a  Hydroxylamine  Derivative  to  a 
Nitroso-Compound        .........     223 

4.  Reaction :  Reduction  of  a  Nitro-Compound  to  an  Azoxy-,  Azo-,  and 

Hydrazo-Compound 226 

5.  Reaction :  Preparation  of  a  Thiourea  and  a  Mustard  Oil  from  Car- 

bon Disulphide  and  a  Primary  Amine 232 

6.  Reaction  :  Sulphonation  of  an  Amine 235 

7.  Reaction :   Replacement  of  the  Amido-  and  Diazo-Groups  by  Hy- 

drogen         „ 237 


CONTENTS  xv 


PAGE 


8.  Reaction  :  Replacement  of  the  Diazo-Group  by  Hydroxyl       .         .  243 

9.  Reaction  :   Replacement  of  a  Diazo-Group  by  Iodine        .         .         .  '  244 

10.  Reaction  :   Replacement  of  a  Diazo-Group  by  Chlorine,  Bromine,  or 

Cyanogen 248 

11.  Reaction:   (#)   Reduction  of  a  Diazo-Compound  to  a  Hydrazine. 

(^)   Replacement  of  the  Hydrazine- Radical  by  Hydrogen  .         .  250 

12.  Reaction:   (0)  Preparation  of  an  Azo-Dye  from  a  Diazo-Compound 

and  an  Amine.     ($)   Reduction  of  the  Azo-Compound         .         .  256 

13.  Reaction:   Preparation  of  a  Diazoamido-Compound          .         .         .  262 

14.  Reaction :  The   Molecular  Transformation  of  a  Diazoamido-Com- 

pound into  an  Amidoazo-Compound     .         .         .         .         .  •        .  265 

15.  Reaction:  Oxidation  of  an  Amine  to  a  Quinone      ....  266 

16.  Reaction  :   Reduction  of  a  Quinone  to  a  Hydroquinone  .         .'        .  270 

17.  Reaction:   Bromination  of  an  Aromatic  Compound  .         .         .         .271 

18.  Reaction  :   Fittig's  Synthesis  of  a  Hydrocarbon         ....  276 

19.  Reaction  :   Sulphonation  of  an  Aromatic  Hydrocarbon  (I)       .         .  280 

20.  Reaction :   Reduction  of  a  Sulphonchloride  to  a  Sulphinic  Acid 

or  to  a  Thiophenol 287 

21.  Reaction:   Sulphonation  of  an  Aromatic  Hydrocarbon  (II)     .         .  290 

22.  Reaction  :  Conversion  of  a  Sulphonic  Acid  into  a  Phenol         .         .  293 

23.  Reaction :  Nitration  of  a  Phenol 296 

24.  Reaction :   (#)  Chlorination  of  a    Side-Chain  of  a   Hydrocarbon. 

(£)  Conversion  of  a  Dichloride  into  an  Aldehyde        .         .         .  298 

25.  Reaction :   Simultaneous  Oxidation  and  Reduction  of  an  Aldehyde 

under  the  Influence  of  Concentrated  Potassium  Hydroxide  .         .  303 

26.  Reaction :  Condensation  of  an  Aldehyde  by  Potassium  Cyanide  to 

a  Benzoin 304 

27.  Reaction  :  Oxidation  of  a  Benzoin  to  a  Benzil           ....  306 

28.  Reaction  :  Addition  of  Hydrocyanic  Acid  to  an  Aldehyde        .         .  307 

29.  Reaction:  Perkin's  Synthesis  of  Cinnamic  Acid       ....  313 

30.  Reaction:  Addition  of  Hydrogen  to  an  Ethylene  Derivative   .         .316 

31.  Reaction  :   Preparation  of  an  Aromatic  Acid-Chloride  from  the  Acid 

and  Phosphorus  Pentachloride 3*7 

32.  Reaction  :  The  Schotten-Baumann  Reaction  for  the  Recognition  of 

Compounds  containing  the  Amido-,  Imido-,  or  Hydroxyl-Group  .  318 


xvi  CONTENTS 

» 

PAGE 

33.  Reaction :   (0)   Friedel  and  Crafts'  Ketone  Synthesis,     (b}  Prepa- 

ration  of   an   Oxime.     (<r)   Beckmann's   Transformation    of  an 

Oxime 320 

34.  Reaction :   Reduction  of  a  Ketone  to  a  Hydrocarbon        .         .         .  329 

35.  Reaction:  Aldehyde  Synthesis.     Gattermann-Koch         .         .         .331 

36.  Reaction :  Saponification  of  an  Acid-Nitrile 335 

37.  Reaction :  Oxidation  of  the  Side-Chain  of  an  Aromatic  Compound  337 

38.  Reaction :   Synthesis  of  Oxyaldehydes.     Reimer  and  Tiemann          .  340 

39.  Reaction :  Kolbe's  Synthesis  of  Oxyacids 344 

40.  Reaction :  Grignard's  Reaction,     (a)   Benzo'ic  Acid  from  lodoben- 

zene.     (^)  Benzhydrol  from  lodo-  or  Brombenzene  and  Benz- 

aldehyde 348 

41.  Reaction:  Preparation  of  a  Dye  of  the  Malachite  Green  Series        .  354 

42.  Reaction :  Condensation  of  Phthalic  Anhydride  with  a  Phenol  to 

form  a  Phthalem 357 

43.  Reaction:  Condensation  of  Michler's  Ketone  with  an  Amine  to  a 

Dye  of  the  Fuchsine  Series 364 

44.  Reaction  :  Condensation  of  Phthalic  Anhydride  with  a  Phenol  to  an 

Anthraquinone  Derivative 365 

45.  Reaction:  Alizarin  from  Sodium  /3-Anthraquinonemonosulphonate  367 

46.  Reaction :  Zinc  Dust  Distillation 369 

III.     PYRIDINE  AND   QUINOLINE   SERIES 

1.  Reaction:  The  Pyridine  Synthesis  of  Hantzsch        ....  371 

2.  Reaction :   Skraup's  Quinoline  Synthesis 374 

IV.     INORGANIC   PART 

1.  Chlorine 377 

2.  Hydrochloric  Acid 377 

3.  Hydrobromic  Acid 379 

4.  Hydriodic  Acid        .                                             379 

5.  Ammonia <,         »         .         .         .         .  382 

6.  Nitrous  Acid ....  382 

7.  Phosphorus  Trichloride    .                                    382 

8.  Phosphorus  Oxychloride  ...         0         «         ....  3^4 


CONTENTS  xvii 

PAGE 

9.  Phosphorus  Pentachloride 384 

10.  Sulphurous  Acid       ..........  385 

11.  Sodium 385 

12.  Aluminium  Chloride 386 

13.  Lead  Peroxide  . 388 

14.  Cuprous  Chloride 389 

15.  Determination  of  the  Value  of  Zinc  Dust          .         .         .         ...  390 

INDEX 391 

ABBREVIATIONS 395 

TABLE  FOR  CALCULATIONS  IN  NITROGEN  DETERMINATION    .        .        .    396 


THE   PRACTICAL  METHODS   OF    ORGANIC 
CHEMISTRY 


GENERAL    PART 


THE  compounds  directly  obtained  by  means  of  chemical  reac- 
tions are,  only  in  rare  cases,  pure ;  they  must  therefore  be 
subjected  to  a  process  of  purification  before  they  can  be  further 
utilised.  For  this  purpose  the  operations  most  frequently  em- 
ployed are  : 

1 .  CRYSTALLISATION. 

2.  SUBLIMATION. 

3.  DISTILLATION. 

CRYSTALLISATION 

Methods  of  Crystallisation.  —  The  crude  solid  product  obtained 
directly  as  the  result  of  a  reaction  is  generally  amorphous  or  not 
well  crystallised.  In  order  to  obtain  the  compound  in  uniform, 
well-defined  crystals,  as  well  as  to  separate  it  from  impurities  like 
filter-fibres,  inorganic  substances,  by-products,  etc.,  it  is  dissolved, 
usually  with  the  aid  of  heat,  in  a  proper  solvent,  filtered  from  the 
impurities  remaining  undissolved,  and  allowed  to  cool  gradually. 
The  dissolved  compound  then  separates  out  in  a  crystallised  form, 
while  the  dissolved  impurities  are  retained  by  the  mother-liquor. 
(Crystallisation  by  Cooling?)  Many  compounds  are  so  easily 
soluble  in  all  solvents,  even  at  the  ordinary  temperature,  that 
they  do  not  separate  from  their  solutions  on  mere  cooling.  In 
this  case,  in  order  to  obtain  crystals,  a  portion  of  the  solvent  must 
be  allowed  to  evaporate.  {Crystallisation  by  Evaporation^} 


2  GENERAL   PART 

Solvents.  —  As  solvents  for  organic  compounds,  the  following 
substances  are  principally  used : 

CLASS  I.     Water, 
Alcohol, 
Ether, 

Ligroin  (Petroleum  Ether), 
Glacial  Acetic  Acid, 
Benzene. 

Also  mixtures  of  these  : 

CLASS  II.  Water  +  Alcohol, 

Water  -f  Glacial  Acetic  Acid, 
Ether  -f  Ligroin, 
Benzene  -f  Ligroin. 

Less  frequently  used  than  these  are  :  hydrochloric  acid,  carbon 
disulphide,  acetone,  chloroform,  ethyl  acetate,  methyl  alcohol, 
amyl  alcohol,  toluene,  xylene,  solvent  naphtha,  etc. 

But  rarely  used  are :  pyridine,  naphthalene,  phenol,  nitro- 
benzene, aniline,  and  others. 

Choice  of  the  Solvent.  —  The  choice  of  a  suitable  solvent  is 
often  of  great  influence  upon  the  success  of  an  experiment,  in  that 
a  solid  compound  does  not  assume  a  completely  characteristic 
appearance  until  it  is  uniformly  crystallised.  In  order  to  find  the 
most  appropriate  solvent,  preliminary  experiments  are  made  in 
the  following  manner :  successive  small  portions  of  the  finely 
pulverised  substance  (a  few  milligrammes  will  suffice)  are  treated 
in  small  test-tubes,  with  small  quantities  of  the  solvents  of  Class  I. 
If  solution  takes  place  at  the  ordinary  temperature,  or  on  gentle 
heating,  the  solvent  in  question  is,  provisionally,  left  out  of  con- 
sideration. The  remaining  portions  are  heated  to  boiling,  until, 
after  the  addition  of  more  of  the  solvent  if  necessary,  solution 
takes  place.  The  tubes  are  now  cooled  by  contact  with  cold 
water,  and  an  observation  will  show  in  which  tube  crystals  have 
separated  in  the  largest  quantity.  At  times  crystallisation  does 
not  occur  on  mere  cooling;  in  this  case  the  walls  of  the  vessel 


CRYSTALLISATION  3 

are  rubbed  with  a  sharp-angled  glass  rod,  or  the  solution  is 
"seeded,"  i.e.  a  small  crystal  of  the  crude  product  is  placed  in  the 
solution ;  by  this  means,  crystallisation  is  frequently  induced.  If 
the  individual  solvents  of  Class  I.  are  shown  to  be  unsuitable, 
experiments  are  made  with  the  mixtures,  —  Class  II.  Compounds 
which  are  easily  soluble  in  alcohol  or  glacial  acetic  acid,  and 
which  consequently  do  not  separate  out  on  cooling,  are,  as  a  rule, 
difficultly  soluble  in  water.  In  order  to  determine  whether  a 
separation  of  crystals  will  take  place  on  cooling,  the  hot  solutions 
in  the  pure  solvents  are  treated  with  more  or  less  water,  according 
to  the  conditions.  Substances  easily  soluble  in  ether,  benzene, 
toluene,  etc.,  often  dissolve  in  ligrom  with  difficulty.  Hence 
mixtures  of  these  solvents  can  be  frequently  utilised  with  ad- 
vantage, in  the  manner  just  described.  If  these  experiments  have 
shown  several  solvents  to  be  suitable,  the  portions  under  examina- 
tion are  again  heated  until  solution  takes  place,  and  this  time 
are  allowed  to  cool  slowly.  That  solvent  from  which  the  best 
crystals  separate  in  the  largest  quantity  is  selected  for  the  crystal- 
lisation of  the  entire  quantity  of  the  substance.  If  a  substance 
is  easily  soluble  in  all  solvents,  recourse  must  be  had  to  crystallisa- 
tion by  evaporation,  i.e.  by  allowing  the  different  solutions  to  stand 
some  time  in  watch-glasses.  That  solvent  from  which  crystals 
separate  out  first  is  the  most  suitable.  Frequently  a  compound 
dissolves  in  a  solvent  only  on  heating  and  yet  does  not  crystallise 
out  again  on  cooling;  compounds  of  this  class  are  said  to  be 
"sluggish  "  (trage).  In  this  case,  the  solution  may  be  allowed  to 
stand  for  some  time,  if  necessary  over  night,  in  a  cool  place.  If 
a  compound  is  very  difficultly  soluble,  solvents  with  high  boiling- 
points  are  use'd,  as  toluene,  xylene,  nitrobenzene,  aniline,  phenol, 
and  others.  The  crystals  obtained  in  these  preliminary  experi- 
ments, especially  if  they  are  of  easily  soluble  substances,  are  pre- 
served, so  that  if  from  the  main  mass  of  the  substance  no  crystals 
can  be  obtained,  the  solution  may  be  seeded,  thus  inducing  crystalli- 
sation. The  crystallisation  of  substances  which  boil  without  decom- 
position may  often  be  facilitated  by  first  subjecting  them  to  distillation. 
Substances  that  are  solids  in  the  crude  form,  will  sometimes 


4  GENERAL  PART 

separate  out  as  liquids  from  solvents.  This  may  be  due  to  the 
presence  of  small  quantities  of  water.  In  this  case,  the  solution  in 
ether,  ligroi'n,  benzene,  etc.,  is  heated  with  fused  Glauber's  salt ; 
crystals  will  often  separate  out  when  this  is  filtered. 

To  dissolve  the  Substance.  —  When  water  or  glacial  acetic  acid, 
or  a  solvent  which  is  not  inflammable  or  not  easily  inflammable,  is 
employed,  the  heating  may  be  done  in  a  beaker  on  a  wire  gauze 
over  a  free  flame  if  the  quantity  is  small ;  if  large,  a  flask  is  always 
used.  In  either  case  care  must  be  taken  to  prevent  the  flask  from 
breaking,  by  stirring  up  the  crystals  from  the  bottom  with  a  glass 
rod,  or  by  frequently  shaking  the  vessel.  This  precaution  is 
especially  to  be  observed  when,  on  heating,  the  substance  to  be 
dissolved  melts  at  the  bottom  of  the  vessel.  Alcohol  and  benzene 
may  also  be  heated  in  like  manner  directly  over  a  moderately 
large  flame,  if  the  student  has  already  had  a  sufficient  amount  of 
experience  in  laboratory  work  and  does  not  use  too  large  quanti- 
ties. If  the  liquid  becomes  ignited,  no  attempt  to  extinguish  the 
flame  by  blowing  on  it  should  be  made,  but  the  burner  is  removed 
and  the  vessel  covered  with  a  watch-glass,  a  glass  plate,  or  a  wet 
cloth.  In  working  with  large  quantities  of  alcohol,  benzene,  ether, 
ligroi'n,  carbon  disulphide,  or  other  substances  with  low  boiling- 
points,  they  are  heated  on  a  water-bath  in  a  flask  provided  with  a 
vertical  glass  tube  (air  condenser)  or  a  reflux  condenser.  A  sub- 
stance to  be  crystallised  from  a  solvent  which  is  not  miscible  with 
water  must  be  dried,  in  case  it  is  moist,  before  dissolving.. 

An  error  which  even  advanced  students  too  often  make  in 
crystallising  substances  consists  in  this  :  an  excessive  quantity  of 
the  solvent  is  poured  over  the  substance  at  once.  When  heat  is 
applied,  it  is  true,  solution  takes  place  easily,  but  on  cooling  noth- 
ing crystallises  out.  So  much  of  the  solvent  has  been  taken  that 
it  holds  the  substance  in  solution  even  at  ordinary  temperatures. 
The  result  is  that  a  portion  of  the  solvent  must  be  evaporated  or 
distilled  off,  which  involves  a  loss  of  time  and  substance,  as  well 
as  decomposition  of  the  substance.  The  following  rule  should, 
therefore,  always  be  observed  :  The  quantity  of  solvent  taken  at 
first  should  be  insufficient  to  dissolve  the  substance  completely,  even 


CRYSTALLISATION  5 

on  heating;  then  more  of  the  solvent  is  gradually  added,  until  all  oj 
the  substance  is  just  dissolved.  In  this  way  only  is  it  certain  that 
on  cooling  an  abundant  crystallisation  will  take  place.  If  a  mixt- 
ure of  two  solvents  is  used,  one  of  which  dissolves  the  substance 
easily  and  the. other  with  difficulty,  e.g.  alcohol  and  water,  the 
substance  is  first  dissolved  in  the  former  with  the  aid  of  heat; 
the  heating  is  continued  while  small  amounts  of  the  second  are 
gradually  added  (if  water  is  used  it  is  better  to  add  it  hot)  until 
the  first  turbidity  appearing  does  not  vanish  on  further  heating. 
In  order  to  remove  this  cloudiness,  a  small  quantity  of  the  first 
solvent  is  added.  On  the  addition  of  the  first  portions  of  the 
second  liquid  (water  or  ligroin)  resinous  impurities  separate  out 
at  times ;  in  this  case,  these  are  filtered  off  before  a  further  addi- 
tion of  the  solvent  is  made. 

At  times  it  happens  that  the  last  portions  of  a  compound  will 
dissolve  only  with  difficulty.  The  beginner  often  makes  the  mis- 
take here  of  adding  more  and  more  of  the  solvent  to  dissolve  this 
last  residue,  which  for  the  most  part  generally  consists  of  difficultly 
soluble  impurities,  like  inorganic  salts,  etc.  The  result  of  this  is 
that  on  cooling  nothing  crystallises  out.  In  such  cases  the  diffi- 
cultly soluble  portions  may  be  allowed  to  remain  undissolved,  and 
on  filtering  the  solution  are  retained  by  the  filter. 

Filtration  of  the  Solution.  —  When  a  substance  has  been  dis- 
solved, the  solution  must  next  be  filtered  from  the  insoluble  im- 
purities like  by-products,  filter-fibres,  inorganic  compounds,  etc. 
For  filtration  a  funnel  with  a  very  short  stem  is  generally  used, 
i.e.  an  ordinary  funnel  the  stem  of  which  has 
been  cut  off  close  to  the  conical  portion  (Fig.  i). 
The  funnels  used  in  analytical  operations  have 
the  disadvantage  that  when  a  hot  solution  of 
a  compound  flows  through  the  stem,  it  be- 
comes cooled  to  such  an  extent  that  crystals 
frequently  separate  out,  thus  causing  an  obstruc- 
tion of  the  stem.  The  funnel  with  a  shortened 
stem  or  no  stem  is  prepared  with  a  folded  filter.  In  case  the 
solution  contains  a  substance  that  easily  crystallises  out,  the  filtei 


6  GENERAL  PART 

is  made  of  rapid-filtering  paper  (Fig.  2).  The  solution  to  be 
filtered  is  not  allowed  to  cool  before  filtering,  but  is  poured  on 
the  filter  immediately  after  removing  it  from  the 
flame  or  water-bath.  If  inflammable  solvents 
are  used,  care  must  be  taken  that  the  vapours 
are  not  ignited  by  a  neighbouring  flame.  Under 
normal  conditions,  no  crystals  or  only  a  few 
should  separate  out  on  the  filter  during  filtra- 
tion. If  large  quantities  of  crystals  appear  in  a 
solution  as  soon  as  it  is  poured  on  the  filter,  it  is 
an  indication  that  too  small  an  amount  of  the  solvent  has  been 
used.  In  a  case  of  this  kind,  the  point  of  the  filter  is  pierced  and 
the  crystals  are  washed  into  the  unfiltered  portion  of  the  solution 
with  a  fresh  quantity  of  the  solvent ;  the  solution  is  further  diluted 
with  the  solvent,  heated,  and  filtered. 

Very  difficultly  soluble  compounds  crystallise  during  the  filtra- 
tion in  the  space  between  the  filter  and  funnel,  in  consequence 
of  the  contact  of  the  solution  with  the  cold  walls  of  the  funnel. 

This  may  be  prevented  when  a  small  quantity  of  liquid  is  to  be 
filtered,  by  warming  the  funnel  previously  in  an  air-bath,  or  directly 
over  a  flame.  If  the  quantity  of  the  liquid  is  large,  hot  water  or 
hot  air  funnels  may  be  used  (Figs.  3  and  4),  or  the  funnel  may 
be  surrounded  by  a  cone  of  lead  tubing  wound  around  it  through 
which  steam  is  passed  (Fig.  5).  Before  filtering  inflammable 
liquids,  the  flame  with  which  the  hot  water  or  hot  air  funnel  has 
been  heated  is  extinguished.  Substances  which  easily  crystallise 
out  again,  may  also  be  conveniently  filtered  with  the  aid  of  suc- 
tion and  a  funnel  having  a  large  filtering  surface  (Biichner  funnel, 
see  Fig.  38,  p.  58).  After  filtration  the  solution  is  poured  into  the 
proper  crystallisation  vessel.  In  order  to  prevent  the  thick- walled 
filter-flasks  from  being  cracked  by  solvents  of  a  high  boiling-point, 
they  are  somewhat  warmed  before  filtering  by  immersion  in  warm 
water. 

Boiling  nitrobenzene,  aniline,  phenol,  and  similar  substances  may 
be  filtered  in  the  usual  way  through  ordinary  filter-paper. 

Choice  of  the  Crystallisation  Vessel. — The  size  and  form  of  the 


CRYSTALLISATION  7 

crystallisation  vessel  is  not  without  influence  upon  the  separation 
of  the  crystals.  If  a  compound  will  crystallise  out  on  simple  cool- 
ing, without  the  necessity  of  evaporating  a  portion  of  the  solvent, 
a  beaker  is  used  for  the  crystallisation.  The  shallow  dishes  known 
as  "  crystallising  dishes  "  are  not  recommended  for  this  purpose, 
since  they  cannot  be  heated  over  a  free  flame,  and  further,  the 
solution  easily  "  creeps  "  over  the  edge,  involving  a  loss  of  the 
substance.  Moreover,  the  crusts  collecting  on  the  edges  are  very 
impure,  since,  in  consequence  of  the  complete  evaporation  of  the 
solvent,  they  contain  all  the  impurities  which  should  remain  dis- 


FIG.  3.  FIG.  4.  FIG.  5. 

solved  in  the  mother-liquor.  The  beaker  is  selected  of  such  a 
size  that  the  height  of  the  solution  placed  in  it  is  approximately 
equal  to  the  diameter  of  the  vessel,  which  is  thus  about  one-half 
to  two-thirds  filled. 

Heating  after  Filtration.  —  Many  compounds  crystallise  out  in 
the  beaker  during  filtration.  The  crystals  thus  obtained  are  never 
well  formed,  in  consequence  of  the  rapid  separation ;  therefore, 
after  the  entire  solution  has  been  filtered,  it  is  heated  again  until 
the  crystals  have  redissolved,  and  is  then  allowed  to  cool  as  slowly 


8  ,  GENERAL   PART 

as  possible  without  being  disturbed.  In  order  to  protect  the  solu- 
tion from  dust  as  well  as  to  prevent  it  from  cooling  too  rapidly,  the 
vessel  is  covered  first  with  a  piece  of  filter-paper  and  then  with  a 
watch-glass  or  glass  plate."  The  paper  is  used  to  prevent  drops  of 
the  solvent  formed  by  the  vapours  condensing  on  the  cold  cover- 
glass  from  falling  into  the  solution,  by  which  the  crystallisation 
would  be  disturbed.  The  paper  need  not  be  used  if  the  vessel  is  cov- 
ered with  a  watch-glass,  the  convex  surface  of  which  is  uppermost : 
the  condensed  vapours  will  thus  flow  down  the  walls  of  the  beaker. 
Crystallisation.  —  In  order  to  obtain  as  good  crystals  as  possible, 
the  solution  is  allowed  to  cool  slowly  without  being  disturbed.  In 
exceptional  cases  only  is  it  placed  in  cold  water  to  hasten  the  separa- 
tion of  crystals.  The  vessel  must  not  be  touched  until  the  crystalli- 
sation is  ended.  If  a  substance,  on  slow  cooling,  separates  out  in 
very  coarse  crystals,  it  is  expedient,  in  case  a  sample  of  the  substance 
for  analysis  is  desired,  to  accelerate  the  crystallisation  by  artificial 
cooling,  so  that  smaller  crystals  will  separate  out.  Very  coarse 
crystals  are  commonly  more  impure  than  smaller  ones,  in  that  they 
enclose  portions  of  the  mother- liquor.  If  a  deposit  of  crystals  as 
abundant  as  possible  is  desired,  the  vessel  is  put  in  a  cool  place  — - 
in  a  cellar  or  ice-chest  if  practicable.  Should  a  compound  crys- 
tallise sluggishly,  the  directions  given  on  page  2,  under  "  Choice  of 
the  Solvent,"  may  be  followed  (rubbing  the  sides  of  the  vessel  with 
a  glass  rod  ;  seeding  the  solution  ;  allowing  to  stand  over  night). 
At  times  a  compound  separates  out  on  cooling,  not  in  crystals,  but 
in  a  melted  condition.  This  may  be  caused  by  the  solution  being 
so  concentrated  that  crystallisation  already  takes  place  at  a  tem- 
perature above  the  fusing-point.  In  this  case  the  solution  is  again 
heated  until  the  oil  which  has  separated  out  is  dissolved,  more  of 
the  solvent  is  then  added,  the  quantity  depending  upon  the  condi- 
tions. In  other  cases  this  may  be  prevented  by  rubbing  the  walls 
of  the  vessel  a  short  time  with  a  sharp-edged  glass  rod,  as  soon  as 
a  slight  turbidity  shows  itself,  or  by  seeding  the  solution  with  a 
crystal  of  the  same  substance.  This  difficulty  may  also  be  avoided, 
in  many  cases,  by  allowing  the  solution  to  cool  very  slowly  ;  e.g.  the 
beaker  is  placed  in  a  larger  vessel  filled  with  hot  water  and  allowed 
to  cool  in  this. 


CRYSTALLISATION  9 

At  times  the  separation  of  crystals  takes  place  suddenly,  within  a 
few  seconds,  throughout  the  entire  solution.  Since  the  crystals  thus 
obtained  are  generally  not  well  formed,  the  liquid,  after  some  of  the 
crystals  have  been  removed,  is  heated  until  solution  again  takes  place. 
After  it  has  partially  cooled,  those  crystals  which  were  taken  out 
are  now  added  to  it,  by  which  a  gradual  crystallisation  is  caused. 

Separation  of  Crystals  from  the  Mother-Liquor.  —  When  crystals 
have  been  deposited,  they  are  then  to  be  separated  from  the  liquid 
(mother-liquor).  This  is  always  done  with  the  aid  of  suction,  and 
never  by  merely  pouring  off  the  liquid.  The  filter  to  be  used  is 
previously  moistened  with  the  same  substance  which  was  employed 
as  the  solvent.  Crusts,  formed  on  the  sides  and  edges  of  the  ves- 
sel by  the  complete  evaporation  of  the  solvent,  are  not  filtered 
with  the  crystals  ;  they  are  removed  with  a  spatula  before  the  filter- 
ing, and  are  worked  up  with  the  mother-liquor.  In  order  to  re- 
move the  last  traces  of  the  mother-liquor  adhering  to  the  crystals, 
they  are  washed  several  times  with  fresh  portions  of  the  solvent ; 
obviously,  if  the  substance  is  easily  soluble,  too  large  quantities  of 
the  solvent  must  not  be  used.  If  a  solvent  that  will  not  evaporate 
easily  in  the  air  or  on  the  water-bath  has  been  used,  e.g.  glacial 
acetic  acid,  toluene,  nitrobenzene,  etc.,  it  must  be  removed  from 
the  crystals  by  a  more  volatile  substance,  like  alcohol  or  ether. 
This  is  done  by  first  washing  with  a  fresh  quantity  of  the  solvent, 
then  with  a  mixture  of  the  solvent  and  a  small  quantity  of  the  more 
volatile  liquid,  the  proportion  of  the  latter  in  the  washing  mixture  be- 
ing gradually  increased,  until  finally  the  volatile  substance  is  used 
alone.  Glacial  acetic  acid  may,  in  this  way,  be  displaced  by  water. 

Drying  of  Crystals. — When  crystals  have  been  freed  from  the 
mother-liquor  they  must  be  dried.  This  may  be  effected  (i)  at 
the  ordinary  temperature  by  the  gradual  evaporation  of  the  solvent 
in  the  air,  and  (2)  at  higher  temperatures  by  heating  on  a  water- 
bath  or  in  an  air-bath.  In  the  first  case  the  crystals  are  spread 
out  in  a  thin  layer  upon  several  thicknesses  of  filter-paper  and 
covered  with  a  watch-glass,  funnel,  beaker,  or  similar  vessel.  In 
order  that  the  vapours  of  the  solvent  may  escape,  the  covering  must 
be  so  placed  that  the  air  is  not  shut  off  completely  from  the  crys- 


IO  GENERAL   PART 

tals ;  this  is  conveniently  done  by  supporting  it  on  several  corks. 
Crystals  may  also  be  dried  in  a  desiccator  which  is  partially  ex- 
hausted, if  necessary.  In  drying  substances  at  higher  temperatures 
the  crystal  form  may  be  lost  by  the  fusion  of  the  substance  or  by 
the  separation  of  the  water  of  crystallisation.  Since  many  sub- 
stances will  liquefy  far  below  their  melting-point  if  they  contain 
even  small  quantities  of  the  solvent,  a  preliminary  experiment  with 
a  small  portion  is  always  made  when  the  drying  is  to  be  effected 
at  higher  temperatures.  Compounds,  not  easily  soluble  in  ether, 
which  crystallise  from  a  solvent  miscible  with  ether,  can  be  very 
quickly  dried  by  being  washed  several  times  with  it.  After  a 
short  exposure  to  the  air  they  are  dry. 

Treatment  of  the  Mother-Liquor.  —  The  mother-liquor  filtered 
off  from  crystals  still  contains  more  or  less  of  the  substance,  in 
proportion  to  its  solubility  at  the  ordinary  temperature ;  in  many 
cases  it  is  advantageous  to  extract  the  last  portions  remaining  in 
solution.  A  "  second  crystallisation  "  is  obtained  by  distilling  or 
evaporating  off  a  portion  of  the  solvent.  The  mother-liquor  may 
also  be  diluted  with  a  second  liquid,  in  which  the  dissolved  sub- 
stance is  difficultly  soluble ;  e.g.  a  solution  in  alcohol  or  glacial 
acetic  acid  may  be  diluted  with  water,  or  a  solution  in  ether  or 
benzene  with  ligroi'n. 

Crystallisation  by  Evaporation.  —  If  a  compound  is  so  easily 
soluble  in  all  solvents  that  it  will  only  crystallise  out  on  partial 
evaporation,  then,  in  order  to  get  good  crystals,  a  solution,  not 
too  dilute,  is  made,  by  the  aid  of  heat  if  necessary,  and  filtered 
from  the  impurities  remaining  undissolved.  In  this  case,  as  a 
crystallisation  vessel,  one  of  the  various  forms  of  shallow  dishes  — 
the  so-called  crystallising  dishes  —  is  used,  in  which  the  solution 
is  allowed  partially  to  evaporate.  In  order  to  protect  the  vessel 
from  dust,  it  is  covered  with  a  funnel  or  watch-glass,  in  the 
manner  indicated  under  "Drying  of  Crystals."  In  crystallising 
by  this  method,  it  sometimes  happens  that  the  solution,  owing  to 
capillary  action,  will  "  creep  "  over  the  edge  of  the  dish.  To 
avoid  loss  of  the  substance  from  this  source,  the  dish  is  placed  on 
a  watch-glass  or  glass  plate.  Under  these  conditions,  the  vessel 


CRYSTALLISATION  I X 

is  never  covered  with  filter-paper,  since,  after  standing  some  time, 
it  may  absorb  the  entire  quantity  of  the  substance.  If,  in  order 
to  obtain  well-formed  crystals,  the  solvent  is  to  be  evaporated  as 
slowly  as  possible  the  solution  is  placed  in  a  beaker  or  test-tube, 
which  is  then  loosely  covered  with  filter-paper.  Evaporation  may 
be  hastened  by  placing  the  crystallisation  vessel  in  a  desiccator, 
charged,  according  to  the  nature  of  the  solvent,  with  different  sub- 
stances ;  for  the  absorption  of  water  or  alcohol,  calcium  chloride 
or  sulphuric  acid  is  used  ;  glacial  acetic  acid  is  absorbed  by  soda 
lime,  solid  potassium  hydroxide,  or  sodium  hydroxide.  The  evap- 
oration.of  all  solvents  may  be  hastened  by  exhausting  the  desiccator. 

Since  the  purifying  effect  of  crystallisation  depends  upon  the 
fact  that  the  impurities  remain  dissolved  in  the  mother-liquor,  and 
with  this  are  filtered  off,  in  no  case  must  the  solvent  be  allowed 
to  evaporate  completely,  but  the  crystals  must  be  filtered  off  while 
still  covered  with  the  mother-liquor.  Before  filtering,  crusts  depos- 
ited, generally  on  the  edges  of  the  vessel,  are  removed  with  the 
aid  of  a  small  piece  of  filter-paper  or  a  spatula.  Even  though 
the  substance  is  very  soluble,  the  mother-liquor  adhering  to  the 
crystals  is  washed  away  with  small  quantities  of  the  solvent.  If 
the  quantity  of  crystals  is  very  small,  the  adhering  mother-liquor 
may  be  separated,  in  cases  of  necessity,  by  placing  them  on  porous 
plates  and  moistening  with  a  spray  of  the  solvent. 

Fractional  Crystallisation.  —  Up  to  this  point,  it  has  been 
assumed  that  the  substance  to  be  crystallised  possessed  an  essen- 
tially homogeneous  nature,  and  the  object  of  crystallisation  was 
only  to  change  it  to  a  crystallised  form.  Crystallisation  is  often 
employed  for  another  purpose  —  that  of  separating  a  mixture  of 
different  substances  into  its  individual  constituents,  —  a  task  that 
is  generally  far  more  difficult  than  the  crystallisation  of  an  individ- 
ual substance.  The  simplest  case  is  one  in  which  two  substances 
are  to  be  separated.  If  the  solubilities  of  the  two  substances  are 
very  different,  as  is  generally  the  case  when  a  mixture  of  two  dif- 
ferent highly  substituted  compounds  is  under  examination,  it  is 
frequently  not  difficult  to  find  a  solvent  which  will  dissolve  a  con- 
siderable portion  of  the  more  easily  soluble  substance,  and  but  a 


12 


GENERAL   PART 


small  portion  of  the  less  soluble.  If,  now,  the  mixture  be  treated 
with  such  a  solvent,  in  not  too  large  quantities,  a  solution  will  be 
obtained  containing  all  of  the  easily  soluble  substance  and  a  small 
portion  of  the  difficultly  soluble  substance. 
This  is  filtered  from  the  residue  remaining 
undissolved.  The  mixture  has  thus  been 
divided  into  two  fractions.  By  evaporating 
the  solution  to  a  certain  point,  the  more  in- 
soluble compound  will  crystallise  out,  unac- 
companied by  any  of  the  other  compound  ; 
the  crystals  are  filtered  off,  and  the  solution 
further  evaporated.  If  the  crystallisation  of 
the  two  fractions  be  repeated  a  second  time, 
a  complete  separation  will  be  effected.  For 
separating  a  mixture  of  this  kind,  specially 
constructed  apparatus  —  the  so-called  ex- 
traction apparatus  —  may  be  employed,  the 
use  of  which  possesses  the  advantage  over 
the  method  of  simple  heating,  that  much 
smaller  quantities  of  the  solvent  are  required. 
An  apparatus  of  this  kind  is  represented  in 
Figs.  6  and  7.  To  a  wide  glass  tube  d  is 
fused  a  narrow  tube  which  acts  as  a  siphon, 
bent  as  in  Fig.  7.  This  portion  of  the 
apparatus  is  surrounded  by  a  glass  jacket  b, 
narrowed  at  its  lower  end.  This  is  con- 
nected with  the  flask  that  is  to  contain  the 
FIG.  6.  FIG.  7.  soivent  A  cork  bearing  a  reflux  condenser 

—a  ball  condenser  is  convenient  —  is  fitted  in  the  opening  at  the 
apper  end  of  the  jacket.  A  shell  of  filter-paper  is  next  prepared 
in  the  following  manner :  Three  layers  of  filter-paper  are  rolled 
around  a  glass  tube  with  half  the  diameter  of  the  inner  tube  d. 
One  end  of  the  roll  must  extend  somewhat  beyond  the  edge  of  the 
glass  tube ;  this  is  turned  over  and  securely  fastened  with  thread. 
To  preserve  the  form  of  the  roll,  thread  is  loosely  wound  around  its 
middle  and  upper  portion.  The  length  of  the  roll  is  such  that  it 


CRYSTALLISATION  1 3 

extends  i  cm.  above  the  highest  point  of  the  narrow  siphon-tube. 
In  the  shell  is  placed  the  mixture  of  the  easily  soluble  and  diffi- 
cultly soluble  substance  to  be  extracted  ;  the  upper  end  is  closed 
by  a  loose  plug  of  absorbent  cotton.  The  flask  a,  containing  the 
solvent,  is  now  heated  on  a  water-bath  or  over  a  free  flame,  accord- 
ing to  the  nature  of  the  solvent.  The  condensed  vapours  drop  from 
the  condenser  into  the  shell,  dissolve  the  substance,  filter  through 
the  paper,  and  fill  the  space  between  shell  and  inner  glass  tube. 
As  soon  as  the  liquid  has  reached  the  highest  point  of  the  siphon- 
tube,  the  solution  siphons  off  and  flows  back  into  the  flask  a. 
This  operation  may  be  continued  as  long  as  necessary.  The 
amount  of  solvent  used  should  be  one  and  a  half  or  two  times 
the  volume  of  the  inner  tube  up  to  the  highest  point  of  the  siphon. 
The  construction  of  a  ball  condenser  is 
.represented  in  Fig.  8.  In  order  to  dis- 
tinguish the  tube  by  which  the  water  en- 
ters from  the  outlet-tube,  the  former  is 
marked  with  an  arrow.  Comparatively 
easy  also  is  the  separation  of  two  sub- 
stances about  equally  soluble,  if  the  one 

is  present  in  larger  quantity  than  the  other.    0  ~~~/J^^\  r^\^~~ fl 
If  a  mixture  of  this  kind  is  dissolved,  then, 
on  cooling,  the  substance  which  was  pres- 
ent  in   larger  quantity  generally  crystal- 
lises   out.      Occasionally,    after    standing 
some   time,   crystals   of  the  second   sub- 
stance will   appear ;    under   these   conditions   the   crystallisation 
must   be   carefully  watched,   and    as   soon    as   crystals   differing 
from  those  first  appearing  are  observed,  the  solution  is  filtered 
with  suction  at  once,  even  though  it  is  still  warm. 

If  two  compounds  crystallise  simultaneously  at  the  outset,  as  is 
the  case  when  they  possess  approximately  the  same  solubility  and 
are  present  in  almost  equal  quantities,  they  can  be  separated  me- 
chanically. If,  e.g.,  one  of  the  compounds  crystallises  in  coarse 
crystals,  and  the  other  in  small  ones,  they  may  be  separated  by 
sifting  through  a  suitable  sieve  or  wire  gauze.  A  compound  crys- 


14  GENERAL  PART 

tallising  in  leaflets  can  frequently  be  separated  from  one  crystal- 
lising in  needles  by  a  sieve.  If  these  methods  fail,  the  separation 
may  be  effected  by  picking  out  the  crystals  with  small  pincers  or  a 
quill.  In  all  these  mechanical  operations,  the  crystals  must  be  as 
dry  as  possible. 

In  many  cases,  when  one  of  the  compounds  is  heavier  than  the 
other,  it  is  possible  to  separate  them  by  causing  the  lighter  crystals 
to  rise  to  the  top  of  the  liquid,  by  imparting  to  it  a  rotatory  motion 
by  rapid  stirring  with  a  glass  rod.  The  heavier  compound  collects 
at  the  bottom  of  the  vessel,  and  the  liquid  with  the  lighter  com- 
pound floating  in  it  can  be  poured  off. 

Double  Compounds  with  the  Solvent.  —  Many  substances  crys- 
tallise from  certain  solvents  in  the  form  of  double  compounds, 
composed  of  the  substance  and  the  solvent.  It  is  well  known  that 
many  substances,  in  crystallising  from  water,  combine  with  a  cer- 
tain portion  of  water.  Alcohol,  acetone,  chloroform,  benzene,  and 
others  also  have  the  power  of  uniting  with  other  substances  to 
form  double  compounds.  As  a  familiar  example,  the  combination 
of  triphenylmethane  with  benzene  may  be  mentioned  in  this  con- 
nection. If  double  compounds  of  this  kind  are  heated,  the  com- 
bined solvent  is  generally  vaporised. 

SUBLIMATION 

Much  less  frequently  than  crystallisation,  sublimation  is  used  to 
purify  a  solid  compound.  The  principle  involved  is  this :  A 
substance  is  converted  by  heat  into  the  gaseous  condition.  The 
vapours  do  not  assume  the  liquid  phase  when  they  are  condensed 
on  a  cold  surface,  but  deposit  in  the  form  of  crystals. 

The  sublimation  of  a  small  quantity  of  a  substance  can  be  con- 
veniently effected  between  two  watch-glasses  of  the  same  size. 
The  substance  to  be  sublimed  is  placed  on  the  lower  one,  which  is 
then  covered  with  a  round  filter  perforated  several  times  in  its 
centre  and  projecting  over  the  edges  ;  the  second  watch-glass  with 
its  convex  side  uppermost  is  placed  on  it,  and  the  two  are  held 
together  by  a  watch-glass  clamp.  If  the  lower  glass  is  now  heated 


SUBLIMATION  jcj 

very  slowly  on  a  sand-bath  with  a  free  flame,  the  vaporised  sub- 
stance condenses  on  the  cold  surface  of  the  upper  watch-glass 
in  crystals;  the  filter-paper  prevents  the  very  small,  light  crys- 
tals from  falling  back  on  the  hot  surface  of  the 
lower  glass.  To  keep  the  upper  glass  cool,  it  is 
covered  with  several  layers  of  wet  filter-paper 
or  with  a  small  piece  of  wet  cloth.  If  large 
quantities  of  a  substance  are  to  be  sublimed, 
the  upper  watch-glass  in  the  apparatus  just  de- 
scribed is  replaced  by  a  funnel  somewhat  smaller 
than  the  lower  glass  (Fig.  9).  To  prevent  the 
escape  of  vapours,  the  stem  of  the  funnel  is 
closed  by  a  plug  of  cotton  or  is  covered  with 
a  small  cap  of  filter-paper.  The  apparatus  for  9  FlG 
sublimation  designed  by  Briihl  is  admirably 
adapted  to  the  purpose  for  which  it  is  intended  (Fig.  10).  It 
consists  of  a  hollow  metal  plate  through  which  water  flows.  In 
the  conical  opening  is  placed  a  crucible  containing  the  substance 
to  be  sublimed.  The  plate  is  covered  with  a  concave  glass  dish, 
the  ground  edges  of  which  fit  the  plate  tightly.  The  crucible  is 
heated  directly  with  a  small  flame,  while  cold  water  flows  through 
the  plate.  The  vapours  condense  in  part  on  the  glass  cover,  but 


more  abundantly  on  the  upper  cold  surface  of  the  plate  in  crystals. 
The  glass  cover  is  not  removed  until  the  apparatus  is  completely 
cold. 


1 6  GENERAL   PART 

Sublimations  can  also  be  conducted  in  crucibles,  flasks,  beakers, 
retorts,  tubes,  etc.  The  heating  may  be  done  in  an  air-  or  oil-bath. 
In  order  to  lead  off  the  vapours  rapidly,  a  current  of  an  indifferent 
gas  is  sent  through  the  apparatus. 

Of  late  years  substances  of  high  purity  have  been  obtained  by 
causing  them  to  sublime  in  vacuo.  An  apparatus  devised  for  this 
purpose  is  described  in  ti\z  Journal  fur  praktische  Chemie,  Vol.  78 
(1908),  page  201. 

DISTILLATION 

Kinds  and  Objects  of  Distillation.  —  By  distillation  is  meant  the 
conversion  by  heat  of  a  solid  or  liquid  substance  into  a  vapour  and 
the  subsequent  condensation  of  this.  When  a  solid  is  distilled  it 
does  not  condense  directly  in  crystals,  as  is  the  case  in  sublima- 
tion. The  distillate  is  a  liquid  which  may  solidify  into  a  crystal- 
line mass  on  standing.  When  distillation  is  conducted  at  the 
atmospheric  pressure,  it  is  called  ordinary  distillation;  if  in  a 
partial  vacuum,  vacuum  distillation.  The  object  of  distillation  is 
either  to  test  the  purity  of  an  individual  substance  by  the  determi- 
nation of  its  boiling-point,  or  to  separate  a  mixture  of  substances 
boiling  at  different  temperatures  into  its  constituents.  (Fractional 
Distillation^ 

Distillation  Vessels.  — The  heating  of  the  substance  to  be  dis- 
tilled is  generally  effected  in  a  fractionating  flask  (Figs,  n,  12,  13). 
These  flasks  differ,  not  only  in  size,  but  in  the  diameter  of  the  con- 
densation-tube (side-tube),  as  well  as  in  the  distance  of  the  latter 
from  the  bulb.  In  selecting  a  fractionating  flask  the  following  points 
are  to  be  observed.  For  distillation  at  the  atmospheric  pressure  a 
flask  is  selected  having  a  bulb  of  such  a  size  that  when  it  contains  the 
substance  to  be  distilled  it  will  be  about  two-thirds  filled.  There 
are  two  objections  to  distilling  small  quantities  of  a  substance  from 
a  large  flask :  the  vapours  are  easily  overheated,  thus  giving  a 
boiling-point  that  is  too  high ;  a  loss  of  the  substance  follows,  in 
that,  after  the  distillation  is  finished,  a  larger  volume  of  vapours 
which  condense  on  cooling,  remains  behind  in  the  bulb,  than  if  a 
smaller  flask  had  been  used.  In  the  distillation  of  low  boiling 


DISTILLATION  1^ 

compounds,  a  flask  is  selected  which  has  its  condensation-tube  as 
high  as  possible  above  the  bulb,  so  that  the  entire  thread  of  mer- 
cury of  the  thermometer  employed  is  heated  by  the  vapour  of  the 
liquid.  By  using  a  flask  of  this  kind  it  is  not  necessary  to  cor- 
rect the  observed  boiling-point,  as  is  the  case  when  the  mercury 
column  is  not  entirely  surrounded  by  the  vapour.  The  higher  a 
substance  boils,  the  nearer  must  the  side-tube  be  to  the  bulb,  in 


FIG.  it. 


FIG.  13. 


order  that  the  vapours  shall  have  as  little  opportunity  as  possible 
of  condensing  below  the  tube  and  flowing  back  into  the  bulb. 

If  large  quantities  of  a  substance  are  to  be  distilled,  an  ordi- 
nary flask  is  used.  This  can  be  converted  into  a  fractionating 
flask  with  the  aid  of  a  cork  bearing  a  T-tube,  as  illustrated  in 
Fig.  14. 

For  the  distillation  of  solid  substances  which  solidify  in  the 
condensation-tube,  a  fractionating  flask  with  a  wide  side-tube  is 
used. 

A  fractional  distillation  can  also  be  conducted  in  the  fractionating 
flasks  just  described ;  but  the  operation  can  be  carried  out  more 
c 


1 8  GENERAL  PART 

rapidly  and  more  completely  by  the  use  of  apparatus  especially 
adapted  to  fractionating  (Fig.  15).  These  can  be  fused  directly 
on  the  bulb  or  they  can  be  attached  to  an  ordinary  flask  by  means 
of  a  cork  (Fig.  14)  ;  the  round,  short-necked  flasks  such  as  rep- 
resented in  Fig.  1 6,  are  well  adapted  to  this  purpose.  Flasks  ol 


FIG.  14. 


FIG.  15. 

Fractionating  Apparatus. 

WURTZ  LlNNEMANN  HEMPEL 


this  description  can  be  obtained  in  different  sizes  but  still  possess 
ing  the  same  width  of  neck ;  this  enables  one  to  use  the  same 
cork  with  any  flask.  The  value  of  these  different  forms  of  fraction- 
ating apparatus  depends  upon  the  fact  that  the  higher  boiling 
portions  carried  along  with  the  vapours  do  not  pass  immediate!) 


DISTILLATION  Xg 

to  the  outlet  tube,  but  before  entering  this  they  have  an  oppor- 
tunity of  condensing  and  flowing  back  into  the  flask.  In  the 
apparatus  of  Wurtz  (a)  the  condensation  takes  place  on  the  large 
upper  surfaces  of  the  bulbs.  More  complete  condensation  is  ob- 
tained in  Linnemann's  apparatus  (b),  which  differs  from  that  of 
Wurtz  in  that  the  narrow  tubes  between  the  bulbs  contain  small 
platinum-wire  sieves.  Since  the  lower 
boiling  portions  condense  to  a  liquid 
and  collect  in  these,  the  ascending 
vapours  are  so  far  cooled  by  the  pas- 
sage through  them  that  the  accom- 
panying portions  of  the  higher  boiling 
substances  are  likewise  condensed. 
The  apparatus  of  Hempcl  is  filled  with 
glass  beads  which  act  like  the  sieves  in 
the  Linnemann  apparatus.  For  the 
distillation  of  large  quantities  of  a 
liquid  the  Hempel  apparatus  is  par- 
ticularly well  adapted  ;  in  working  with 
it  as  well  as  the  Linnemann  form,  the 
heating  must  be  interrupted  from  time 
to  time,  in  order  that  the  liquid  col-  'IGt  l6' 

lecting  in  the  beads  or  sieves  may  have  an  opportunity  to  flow 
back  to  the  distillation  flask.  If  the  Le  Bel-Henninger  form  is 
used,  this  precaution  is  unnecessary,  since  in  this  apparatus 
special  tubes  for  conducting  off  the  condensed  liquid  are  joined 
to  the  sides  of  the  bulb  somewhat  above  the  sieves. 

Experiments  have  shown  that  a  single  distillation  with  one  of  the 
forms  of  apparatus  just  described,  effects  a  more  complete  separa- 
tion than  repeated  fractionations  in  an  ordinary  fractionating  flask. 

Supporting  the  Fractionating  Flask.  —  If  it  is  necessary  to 
support  the  fractionating  flask  with  a  clamp,  it  is  placed  as  far 
above  the  outlet  tube  as  possible,  never  below  it ;  the  glass  ex- 
pands by  contact  with  the  hot  vapours,  and  since  the  expansion 
is  impeded  by  the  clamp,  particularly  if  it  is  firmly  attached,  the 
flask  frequently  breaks. 


20  GENERAL  PART 

Supporting  the  Thermometer.  —  The  thermometer  is  passed 
through  a  cork  (no  rubber)  which  fits  the  neck  of  the  flask.  The 
most  exact  determinations  of  the  boiling-point  are  obtained  if  the 
entire  thread  of  mercury  is  surrounded  by  the  vapour  of  the  sub- 
stance. With  low  boiling  compounds  this  condition  is  easily 
obtained  by  the  use  of  a  fractionating  flask  having  its  outlet  tube 
at  a  sufficient  distance  above  the  bulb.  In  this  case  the  ther- 
mometer is  so  placed  that  the  degree  corresponding  to  the  boil- 
ing-point of  the  liquid  is  opposite  the  outlet  tube,  but  the  bulb 
of  the  thermometer  must  not  extend  into  the  bulb  of  the  flask 
and  never  into  the  liquid  ;  if  it  does,  another  flask  must  be  used, 
the  outlet  tube  of  which  is  still  higher  above  the  bulb.  If  in 
dealing  with  high  boiling  compounds  such  an  arrangement  is 
not  possible,  the  thermometer  is  thrust  so  far  into  the  neck  of  the 
flask  that  the  thermometer-bulb  is  somewhat  below  the  outlet 
tube.  In  this  case,  if  an  exact  determination  of  the  boiling-point 
is  desired,  the  observed  reading  is  corrected  in  the  manner 
described  below.  In  order  to  avoid  making  a  correction  a  special 
form  of  thermometer  is  used,  the  graduation  of  the  scale  begin- 
ning at  1 00°,  200°,  or  at  other  convenient  points.  By  employing 
an  instrument  of  this  kind  the  mercury  column  may  be  kept  in 
the  vapours  at  any  temperature. 

In  making  distillations,  it  occasionally  happens  that  the  mercury 
column  ascends  to  that  point  in  the  scale  which  is  hidden  by  the 
cork  supporting  the  thermometer,  thus  preventing  the  temperature 
from  being  read.  In  a  case  of  this  kind  the  thermometer  is 
either  raised  or  lowered,  so  that  the  top  of  the  mercury  is  visible, 
or  if  this  is  not  possible,  from  that  portion  of  the  cork  which  pro- 
jects above  the  flask,  a  section  is  cut  which  will  enable  the  scale 
to  be  seen. 

Condensation  of  Vapours.  —  The  condensation  of  vapours  is 
effected  in  various  ways,  depending  upon  the  height  of  the  boiling- 
point.  If  a  compound  boils  at  a  relatively  low  temperature  (up  to 
100°),  the  outlet  tube  of  the  fractionating  flask  is  connected  with 
a  Liebig  condenser  by  a  cork  (not  a  rubber  stopper) .  For  very 
low  boiling  compounds  a  long  condenser  is  used,  and  for  those  of 


DISTILLATION 


21 


high  boiling-points  a  short  one.  If  the  boiling-pomi  of  a  com- 
pound is  very  low,  the  flask  in  which  the  condensed  liquid  collects 
(the  receiver)  is  connected  with  the  condenser  by  means  of  a  cork 
and  a  bent  adapter  (Fig.  63),  and  the  receiver  is  cooled  by  ice 
or  a  freezing  mixture.  If  the  boiling-point  is  moderately  high, 
between  100°  and  200°,  the  receiver,  connected  to  the  condensing 
tube  by  a  cork,  is  cooled  by  running  water  (Fig.  17).  If  the 
substance  is  to  be  distilled 
again,  a  fractionating  flask 
is  employed  as  a  receiver;  a 
tubulated  suction-flask  may 
also  be  used.  It  is  often 
unnecessary  to  employ  run- 
ning water  for  cooling  pur- 
poses if  to  the  outlet  tube  of 
the  flask  a  wide  glass  tube 
50  cm.  long  (extension  tube) 
is  connected  by  a  cork  (Fig. 
1 8) .  With  still  higher  boil- 
ing substances  even  this  is 
superfluous,  since  the  con- 
densation tube  of  the  frac- 
tionating flask,  provided  it 
is  not  too  short,  will  suffice 
for  the  condensation. 

If  a  small  quantity  of  a  substance  is  to  be  distilled,  and  it  is 
desired  to  avoid  the  loss  of  substance  necessarily  incident  to  the 
use  of  a  condenser,  the  distillation  even  of  low  boiling  compounds 
is  conducted  in  a  small  distillation  flask  as  slowly  and  carefully 
as  possible,  the  source  of  heat  being  a  minute  flame  (the  so-called 
microburner). 

If  large  quantities  are  to  be  distilled,  a  condenser  is  always  used, 
since  when  other  condensation  apparatus  is  employed,  the  tube 
finally  becomes,  so  hot  that  the  vapours  are  not  completely  con- 
densed. If  the  vapours  of  a  substance  attack  corks,  the  outlet 
tube  is  inserted  far  enough  into  the  condenser  or  extension  tube 


FIG.  17. 


22 


GENERAL   PART 


so  that  the  vapours  do  not  come  in  contact  with  the  cork.  Bui 
generally  a  cork  is  not  used ;  the  outlet  tube  being  inserted  suffi- 
ciently far  into  the  condenser. 

Heating.  —  Low  boiling  substances  (those  boiling  up  to  about 
80°)  are  not  generally  heated  over  the  free  flame,  but  on  the  water- 
bath  gently  or  to  full  boiling.  Frequently  it  is  more  convenient 
to  immerse  the  bulb  of  the  fractionating  flask  as  far  as  the  level 
of  the  liquid  which  it  contains  in  a  dish  or  beaker  filled  with 
water,  which  is  heated  gently  or  strongly  as  the  case  requires. 
Low  boiling  substances  may  also  be  heated  by  immersing  the  bulb 


FIG.  18. 

of  the  flask  from  time  to  time  in  a  vessel  filled  with  warm  water. 
If  a  substance  is  not  distilled  over  a  free  flame,  in  order  to  prevent 
"bumping"  a  few  pieces  of  platinum  wire  or  foil,  or  bits  of  glass, 
are  thrown  into  the  liquid  (see  below).  When  a  substance  to  be 
distilled  is  heated  on  the  water-bath,  it  may  easily  happen  that 
the  vapour  inside  the  flask  may  be  overheated  by  the  steam  escap- 
ing between  the  rings.  For  this  reason,  in  the  determination  of 
exact  boiling-points  it  is  better  to  use  a  small  free  flame.  The 
so-called  microburner  is  well  adapted  to  this  purpose.  High  boil- 


DISTILLATION  23 

ing  substances  are  always  heated  over  the  free  flame.  In  this  case 
the  flask  may  be  protected  by  heating  it  on  a  wire  gauze  ;  still  by 
working  carefully  the  gauze  need  not  be  used.  In  heating,  the 
flame  is  not  placed  under  the  flask  at  once,  since  the  latter  is  likely 
to  break  easily  on  sudden  heating ;  it  is  better  to  pass  the  flame 
back  and  forth  slowly  and  uniformly  over  the  bottom  of  the  flask 
until  the  liquid  is  brought  to  incipient  ebullition.  Substances  which 
have  been  previously  dissolved,  after  the  evaporation  of  the  solvent 
on  the  water-bath,  often  stubbornly  refuse  to  give  up  the  last  por- 
tions of  the  solvent,  particularly  when  ether  has  been  used.  If  now 
a  free  flame  be  applied,  it  frequently  happens  that  in  consequence 
of  a  retarded  boiling  during  which  the  solution  becomes  overheated, 
a  sudden  active  ebullition  and  foaming  will  take  place.  In  order 
to  prevent  this  the  flask  is  shaken  repeatedly  during  the  heating, 
since  if  the  liquid  is  kept  in  motion,  overheating  cannot  easily  take 
place.  It  may  also  be  prevented  frequently  by  heating  the  flask 
on  the  side.  During  the  actual  distillation  the  heating  may  be  con- 
tinued by  slowly  passing  the  flame  over  the  bottom  of  the  flask  as  in 
the  preliminary  heating,  but  in  this  case  care  must  be  taken  not  to 
apply  the  flame  to  the  flask  at  any  point  above  the  liquid  inside, 
since  an  overheating  of  the  vapours  would  result.  In  order  to 
protect  the  hand  in  case  the  flask  should  break,  the  burner  is  held 
obliquely  and  not  directly  under  the  flask  ;  or  during  the  distilla- 
tion the  burner  may  be  placed  under  the  flask  and  allowed  to  re- 
main stationary.  The  size  of  the  flame  is  so  regulated  that  the 
condensed  distillate  flows  into  the  receiver  regularly  in  drops.  If 
vapours  escape  from  the  receiver,  it  is  an  indication  that  the  heat- 
ing is  too  strong.  Toward  the  end  of  the  distillation  the  burner  is 
turned  down  somewhat. 

To  collect  the  Fractions.  —  If  a  substance  which  is  not  quite 
pure  is  being  treated,  and  it  is  desired  to  test  the  purity  by  a 
determination  of  its  boiling-point,  then  on  distillation  a  small  por- 
tion will  generally  pass  over  below  the  true  boiling-point  ("  first 
runnings  ");  this  is  collected  separately  in  a  small  receiver.  Then 
follows  the  principal  fraction,  passing  over  at  the  true  boiling-point, 
the  temperature  remaining  constant.  If  there  is  only  a  small 


24  GENERAL  PART 

quantity  of  the  liquid  in  the  bulb  of  the  flask,  it  is  difficult,  in  spite 
of  using  a  small  flame,  to  prevent  the  vapours  from  being  some- 
what overheated  ;  this  will  cause  a  rise  of  the  mercury  The  por- 
tion passing  over  a  few  degrees  above  the  true  boiling-point  can, 
in  preparation  work,  be  collected  with  that  portion  which  boils  at 
the  correct  temperature,  without  evil  results.  High  boiling  portions 
collected  separately  are  designated  as  "last  runnings."  The  oper- 
ation of  fractional  distillation  is  conducted  in  a  wholly  different 
manner.  The  preparation  of  benzoyl  chloride  (see  page  317) 
will  furnish  a  practical  example  of  the  method  of  procedure.  This 
compound  is  obtained  by  treating  benzoic  acid  with  phosphorus 
pentachloride.  The  product  of  the  reaction  is  a  mixture  of  phos- 
phorus oxychloride  (b.  p.  110°)  and  benzoyl  chloride  (b.  p.  200°). 
If  this  mixture  is  subjected  to  distillation,  the  entire  quantity  of 
phosphorus  oxychloride  does  not  pass  over  at  about  110°,  and 
afterwards  the  benzoyl  chloride  at  200° ;  but  the  distillation  will 
begin  below  110°,  and  a  mixture  consisting  of  a  large  quantity  of 
the  lower  boiling  substance  and  a  small  quantity  of  the  higher 
boiling  substance  will  pass  over ;  the  temperature  then  rises  gradu- 
ally ;  while  the  quantity  of  the  former  steadily  decreases,  that  of 
the  latter  increases,  until  finally,  at  200°,  a  mixture  consisting  essen- 
tially of  the  higher  boiling  substance  passes  over.  A  quantitative 
separation  of  the  constituents  of  a  mixture  cannot  be  effected  by 
the  method  of  fractional  distillation.  However,  in  most  cases,  it 
is  possible  to  obtain  fractions  which  contain  the  largest  part  of 
the  individual  constituents,  particularly  when,  as  in  the  example 
selected,  the  boiling-points  of  the  constituents  lie  far  apart,  by 
collecting  the  different  fractions  and  repeating  the  distillation  a 
number  of  times.  It  is  almost  impossible  to  give  definite  rules  of 
general  application  for  fractional  distillation  ;  the  number  of  frac- 
tions to  be  collected  depends  upon  the  difference  of  the  boiling- 
points,  upon  the  number  of  compounds  to  be  separated,  upon  the 
relative  proportion  of  the  compounds  present,  and  upon  other 
factors.  If  but  two  substances  are  to  be  separated,  as  is  generally 
the  case  in  preparation  work,  the  procedure  is,  very  commonly,  as 
follows :  as  a  basis  for  the  fractions  to  be  collected,  the  interval 


DISTILLATION  25 

between  the  boiling-points  is  divided  into  three  equal  parts  ;  in  the 
case  of  the  example  selected  the  temperatures  would  be  1 10°,  140°, 
170°,  200°.  The  fraction  passing  over  between  the  temperature 
at  which  the  distillation  first  begins,  up  to  140°,  is  collected  (frac- 
tion I.),  then  in  another  vessel  the  fraction  passing  over  between 
140°-!  70°  (fraction  II.),  and  finally  in  another  receiver  that  pass- 
ing over  between  170°  and  200°  (fraction  III.).  The  quantities 
of  the  three  fractions  thus  obtained  are  about  equal.  Fraction  I. 
is  now  redistilled  from  a  smaller  flask,  and  the  portion  passing 
over  up  to  140°  is  collected  as  in  the  first  distillation  in  the  empty 
receiver  I.,  which  in  the  meantime  has  been  washed  and  dried. 
When  the  temperature  reaches  140°,  the  distillation  is  stopped, 
and  to  the  residue  remaining  in  the  flask  is  added  fraction  II.,  and 
the  distillation  continued.  The  portion  passing  over  up  to  140° 
is  collected  in  receiver  I.,  that  from  140°-: 70°  in  the  empty  re- 
ceiver II.  When  the  temperature  reaches  170°,  the  distillation  is 
again  interrupted,  and  to  the  residue  in  the  flask  is  added  fraction 
III.,  and  the  distillation  is  again  continued  :  in  this  way  the  three 
fractions  are  collected.  These  are  again  distilled  as  in  the  first 
distillation,  but  now  the  lower  and  higher  boiling  fractions  are  much 
larger  than  the  intermediate  one  ;  further,  a  larger  portion  of  these 
end  fractions  boil  nearer  the  true  boiling-points  than  in  the  first 
distillation.  If  it  is  now  desired  to  obtain  the  two  substances  in 
question  in  a  still  purer  condition,  the  two  end  fractions  are  once 
more  distilled  separately,  and  the  portion  passing  over  a  few  de- 
grees above  and  below  the  true  boiling-point,  for  phosphorus  oxy- 
chloride  about  105°-!  15°,  for  benzoyl  chloride,  i95°-2O5°  are 
collected. 

Vacuum  Distillation.  —  Many  compounds,  not  volatile  at  the 
atmospheric  pressure  without  decomposition,  may  be  distilled 
undecomposed  in  a  partial  vacuum.  The  vacuum  distillation  is 
used  advantageously  for  the  fractionation  of  small  quantities  of  a 
substance,  since  the  separation  of  the  individual  constituents  can 
be  effected  more  rapidly  and  more  completely  than  at  the  atmos- 
pheric pressure. 

Vacuum  Apparatus.  —  The  simplest  form  of  a  vacuum  apparatus 


26 


GENERAL   PART 


is  represented  in  Fig.  19.  Two  fractionating  flasks  a  and  b  are 
connected  by  a  cork.  The  neck  of  a  is  closed  by  a  tightly  fitting 
cork  bearing  the  glass  tube  d,  reaching  to  the  bottom  of  the  flask, 
its  lower  end  being  drawn  out  to  a  fine  point,  the  object  of  which 
will  be  explained  below.  A  thermometer  is  placed  in  the  tube. 


FIG.  19. 

In  place  of  the  flask  b,  a  suction-flask  such  as  finds  application 
in  filtering  under  pressure,  may  be  used  (Fig.  20).  But  this  kind 
of  flask  is  used  only  in  case  low  boiling  substances  are  to  be 
distilled,  since  the  contact  of  too  hot  liquids  with  the  thick  walls 
causes  them  to  crack  easily  :  this  is  likely  to  prove  very  destructive 
in  vacuum  distillation.  With  low  boiling  substances,  in  order  to 
get  complete  condensation  of  the  vapours,  the  jacket  of  a  Liebig 
condenser  through  which  water  is  allowed  to  flow  is  fitted  over 
the  outlet  tube  of  the  fractionating  flask.  These  simple  forms 
of  apparatus  are  used  only  when  it  is  desired  to  collect  a  few 
fractions,  since  it  is  troublesome  to  be  obliged  to  change  the 
receiver,  and  thus  destroy  the  vacuum,  for  each  new  fraction. 
If  it  is  desired  to  collect  a  larger  number  of  fractions,  an 


DISTILLATION  2; 

apparatus  is  employed  by  means  of  which  the  receiver  can  be 
changed  without  destroying  the  vacuum. 


FIG.  20. 

Briihl's  apparatus  is  very  well  adapted  to  this  purpose  (Figs.  21 
and  22).  By  turning  the  axis  b,  so  arranged  that  it  supports  the 
receivers  firmly,  each  receiver  may  in  turn  be  brought  under  the 
end  of  the  condenser  tube  c. 

The  receiver  shown  in  Fig.  23  is  also  very  convenient  for  frac- 
tional distillation  in  a  vacuum.  By  grasping  the  cork  a  and  the 
tube  c  firmly  with  the  fingers  and  turning,  the  different  portions 
of  the  receiver  may  be  brought  under  the  condensing  tube. 

Construction  of  a  Vacuum  Apparatus.  —  In  vacuum  distillations 
the  evolution  of  bubbles  of  vapour  occurs  to  a  much  greater 
extent  than  under  ordinary  conditions.  In  order  to  prevent  the 
liquid  from  foaming  up  and  passing  over,  a  flask  of  such  a  size  is 
selected,  that  when  it  contains  the  liquid  it  must  in  no  case  be 
more  than  half  full ;  it  is  better  to  have  it  but  one-third  full.  The 
individual  parts  of  the  apparatus  are  connected  by  rubber  stoppers. 
Ordinary  corks  may  also  be  used  with  almost  equally  good  results, 
but  only  those  are  selected  which  are  as  free  as  possible  from 


28 


GENERAL  PART 


pores ;  they  are  pressed  in  a  cork-press,  and  then  very  carefully 
bored.     If,  after  the  apparatus  is  put  together,  the  corks  are  coated 


FIG.  21. 

with  a  thin  layer  of  collodion,  there  is  no  difficulty  in  obtaining  a 
vacuum.     The  thermometer  and  capillary  tube  may  be  arranged  as 

shown  in  Fig.  19.  It  is  also 
a  very  excellent  arrangement 
to  use  a  two-hole  cork,  the 
thermometer  passing  through 
one,  and  the  capillary  tube 
through  the  other,  as  in  Fig. 
21.  The  capillary  tube  is 
made  by  drawing  out  a  glass 
tube  of  1-2  mm.  diameter ; 
the  narrow  hole  in  the  cork 
through  which  this  passes  is 
made  conveniently  by  a  hot 
knitting-needle.  Instead  of 
using  a  capillary  tube  to 
prevent  "  bumping,"  other 


FIG.  22. 


DISTILLATION 


means  may  be  employed  (see  below),  in  which  case  the  ther- 
mometer is  supported  in  the  fractionating  flask  as  in  ordinary 
distillations.  When  a  tube  drawn  out  to 
a  capillary  point  is  used,  a  short  piece  of 
thick-walled  rubber  tubing,  which  can  be 
closed  by  a  screw  pinch-cock  (Fig.  19,  e 
and  c),  is  attached  to  the  upper  end. 

The  flasks  recommended  by  Claisen 
(Fig.  24)  may  be  used  advantageously  in 
vacuum  distillations  in  place  of  the  com- 
mon fractionating  flasks.  A  tube  drawn 
out  to  a  capillary  point  is  secured  in  the 
limb  a  by  a  piece  of  thick-walled  rubber 
tubing  or  a  cork.  The  thermometer  is 
inserted  in  b.  When  a  few  large  pieces  of 
broken  glass  are  placed  in  b,  these  flasks 
possess  the  advantage  of  preventing  por-  FlG  g 

tions  of  the  liquid  (even  in  cases  of  violent 

boiling)  from  being  carried  over  into  the  condenser.     The  space 
above   the   pieces   of   broken   glass   may   be    filled,  partially  or 


FIG.  25. 


FIG.  24. 


wholly,  with  glass  beads  —  obviously  these  are  only  to  be  used  in 
the  distillation  of  liquids  not  having  a  too  high  boiling-point  — 


30  GENERAL   PART 

thus  combining  the  advantages  of  a  Hempel  column  with  vacuum 
distillation. 

For  the  distillation  of  solids  a  fractionating  flask  with  a  wide, 
bent  sabre-shaped  condensing  tube  is  used  (Fig.  25).  In  order 
to  determine  the  efficiency  of  the  vacuum,  the  lower  tube  of  the 
Briihl  apparatus  is  connected  with  a  manometer  (Fig.  26),  by 
means  of  a  thick-walled  rubber  tubing  which  will  not  collapse 
upon  exhausting  the  apparatus.  The  other  end 
of  the  manometer  is  connected  with  suction,  by 
the  same  kind  of  rubber  tubing. 

Since  in  consequence  of  the  varying  water 
pressure,  it  happens,  at  times,  that  the  water  from 
the  suction  pump  may  be  forced  into  the  man- 
ometer or  receiver,  it  is  advisable  to  insert  a 
thick-walled  suction  flask  between  the  suction 
pump  and  manometer. 

In  order  that  the  apparatus  may  be  perfectly 
tight,  the  corks,  ends  of  the  rubber  tubing,  as  well 
as  the  ground  surfaces  of  the  Briihl  receiver,  are 
covered  with  a  thin  layer  of  grease  or  vaseline.  If  ordinary  corks 
are  used,  these,  as  well  as  the  ends  of  the  tubing,  are  covered 
with  collodion  after  the  apparatus  is  set  up.  Before  the  distil- 
lation, the  apparatus  is  tested  to  determine  whether  it  will  give  the 
desired  vacuum.  For  this  purpose,  the  pinch-cock  on  the  capil- 
lary tube  is  closed,  the  suction  attached,  and  after  some  time  the 
manometer  is  read  :  this  will  indicate  whether  the  desired  vacuum 
has  been  obtained.  In  case  it  is  not,  the  corks  are  pressed  more 
firmly  into  the  tubes,  greased  again  or  covered  with  more  collodion, 
and  the  rubber  tubing  is  pushed  farther  over  the  ends  of  the  glass. 
Frequently  the  suction  pump  will  not  work  satisfactorily;  it  is 
then  examined  to  see  if  it  is  stopped  up,  or  a  better  pump  is  used. 
When  the  apparatus  has  been  exhausted,  the  air  must  not  be 
admitted  suddenly,  by  removing  a  rubber  joint,  for  the  sudden 
rushing  in  of  the  air  may  easily  destroy  the  apparatus.  The 
rubber  tube  attached  to  the  suction  is  closed  by  a  screw  pinch- 
cock  which  has  been  placed  on  it  beforehand,  and  in  case  a 


DISTILLATION  3 1 

capillary  tube  has  been  used,  the  pinch-cock  on  this  is  gradually 
opened  and  the  air  allowed  to  enter  through  it,  or  after  discon- 
necting the  rubber  tubing  from  the  suction,  the  pinch-cock  which 
has  just  been  closed  may  be  opened.  The  same  object  may  be 
accomplished  most  rapidly  by  closing  the  tubing  leading  to  the 
suction  with  the  fingers,  detaching  it  and  opening  the  tube  re- 
peatedly for  an  instant  at  a  time,  until  the  rushing  sound  made 
by  the  inflowing  air  ceases.  After  a  test  has  shown  that  the 
apparatus  does  not  leak,  the  liquid  to  be  distilled  is  poured  in 
the  flask  and  the  distillation  begun. 

Heating.  —  In  vacuum  distillation  the  flask  can  be  heated 
directly  with  a  free  flame,  but  the  flame  must  be  applied  to  the 
side,  and  not  to  the  bottom  of  it,  as  in  the  ordinary  way.  Care 
must  be  taken  to  keep  the  flame  constantly  moving.  It  is  much 
more  satisfactory  and  safer  to  use  an  oil-  or  paraffin -bath,  or  better 
a  metallic  air-bath  (iron  crucible).  The  latter  is  covered  with 
a  thick  asbestos  plate  containing  a  round  opening  in  the  centre, 
through  which  the  neck  of  the  fractionating  flask  may  pass ;  from 
the  opening  to  the  edge  of  the  plate  there  is  a  straight  narrow  slit. 
The  air-bath  must  not  be  too  large ;  the  bottom  is  covered  with 
a  thin  layer  of  asbestos,  which  will  prevent  the  flask  from  coming 
in  contact  with  the  metal.  The  temperature  of  the  oil-  or  air- 
bath  should,  in  exact  experiments,  not  be  more  than  2O°-3O° 
higher  than  the  boiling-point  indicated  by  the  thermometer.  A 
thermometer  is  immersed  in  the  bath  and  the  flame  so  regulated 
that  the  difference  between  the  two  thermometers  is  not  greater 
than  that  mentioned.  The  heating  is  not  begun  until  the  appara- 
tus is  exhausted. 

To  prevent  Bumping.  —  In  vacuum  distillations  a  troublesome 
bumping  (a  sudden,  violent  ebullition)  frequently  occurs.  To  pre- 
vent this  a  slow,  continuous  current  of  air  is  drawn  through  the 
Hquid,  thus  keeping  it  in  constant  motion.  The  air  current,  con- 
trolled by  a  pinch-cock,  must  not  be  allowed  to  enter  too  rapidly, 
otherwise  it  will  be  difficult  to  maintain  a  high  vacuum.  The 
same  effect  may  be  obtained  by  placing  certain  substances  in  the 
liquid  —  splinters  of  wood  the  size  of  a  match,  capillary  tubes,  bits 
of  glass,  pieces  of  porcelain,  powdered  talc,  scraps  of  platinum 
wire  or  foil.  Small  pieces  of  pumice-stone  bound  with  platinum 


GENERAL   PART 


wire  also  act  satisfactorily.  For  further  details  concerning  vacuum 
distillation  consult  "  Die  Destination  unter  vermindertem  Druck 
im  Laboratorium,"  R.  Anschtitz. 

Lowering  of  the  Boiling-Point.  —  In  order  that  some  idea  may 
be  obtained  as  to  the  approximate  lowering  of  the  boiling-point, 
by  diminishing  the  pressure,  the  following  table  is  given  : 


Substance. 

Boiling-point  at 
12  mm. 

Boiling-point  at 
Ordinary  Pressure. 

Difference. 

Acetic  acid      

I9° 

118° 

99° 

Monochloracetic  acid    . 

84° 

1  86° 

102° 

Chlorbenzene  

27° 

132° 

I05° 

p-Nitrotoluene      .... 

1  08° 

236° 

128° 

Acetanilide      

I67° 

295° 

128° 

Corrections  of  the  Boiling-Point.  —  If  it  is  not  possible  in 
making  an  exact  determination  of  the  boiling-point  to  have  the 
mercurial  column  entirely  surrounded  by  the  vapour  of  the  liquid, 
—  a  condition  usually  obtained  by  employing  a  flask,  the  side-tube 
of  which  is  at  a  sufficient  distance  from  the  bulb,  or  a  sectional 
thermometer,  or  both,  —  then  a  correction  may  be  applied  to  the 
observed  boiling-point  in  one  of  two  ways.  The  portion  of  the 
mercurial  column  not  heated  by  the  vapours  —  that  portion  above 
the  side-tube  —  is  read  in  degrees  (Z).  Another  thermometer 
is  brought  as  near  as  possible  to  the  middle  point  of  this  col- 
umn, the  temperature  of  which  is  also  read  (/).  If  T  is  the 
observed  boiling  temperature,  then  the  following  correction  is 
added  :  L(T—t} .  0.000154°.  The  so-called  "  corrected  "  boiling- 
point  may  also  be  obtained  as  follows :  The  boiling-point  is 
determined  in  the  usual  way ;  after  the  distillation,  another  sub- 
stance, the  corrected  boiling-point  of  which  is  known,  and  which 
lies  near  the  one  in  question,  is  placed  in  the  same  flask  and  dis- 
tilled under  the  same  conditions.  The  difference  between  the 
corrected  and  observed  boiling-points  is  applied  to  the  boiling- 
point  of  the  first  substance. 

Distilling  oif  a  Solvent. —An  operation  frequently  employed 
in  organic  work  is  distilling  off  a  solvent  from  the  substance  dis- 


DISTILLATION  33 

solved  in  it.  When  the  boiling-point  of  the  solvent  is  sufficiently 
far  away  from  that  of  the  dissolved  substance,  a  complete  separa- 
tion can  be  effected  by  a  single  distillation.  The  methods  used 
depend  upon  the  quantity  of  the  solution,  that  of  the  dissolved 
substance  and  the  boiling-point  of  the  solvent.  The  methods 
which  can  be  used  for  distilling  off  low  boiling  solvents,  like  ether, 
ligroin,  carbon  disulphide,  alcohol,  and  others,  will  be  described 
first.  If  a  small  quantity  of  a  solvent  is  to  be  evaporated,  and  it 
is  not  worth  the  trouble  to  recover  it  by  condensation,  then,  in 
case  the  solvent  is  ether,  ligroin,  or  carbon  disulphide,  the  solution 
is  poured  into  a  small  flask,  and  this  is  immersed  in  a  larger  vessel 
filled  with  warm  water.  The  vaporisation  is  considerably  accel- 
erated by  shaking  the  flask.  The  operation  is  more  rapidly  per- 
formed by  heating  the  flask  on  a  water-bath.  To  prevent  a 
sudden  foaming,  due  to  retarded  ebullition,  some  small  pieces  of 
platinum  wire  or  capillary  tubes  are  placed  in  the  liquid ;  the 
evaporation  is  also  facilitated  by  frequent  shaking.  Should  the 
vapours  become  ignited  from  the  flame  of  the  water-bath,  no 
attempt  to  blow  out  the  burning  vapours  should  be  made;  but 
the  burner  is  extinguished,  the  flask  removed  from  the  bath  with 
a  cloth,  and  the  mouth  covered  with  a  watch-glass.  Carbon  disul- 
phide, on  account  of  its  great  inflammability,  is  never  vaporised 
in  this  way,  but  always  without  a  flame. 

Large  quantities  of  solvents  may  also  be  evaporated  by  these 
two  methods,  but  the  entire  quantity  is  not  treated  at  once.  A 
portion  is  placed  in  a  small  flask,  and  when  this  has  been  evap- 
orated, a  second  portion  is  added,  and  so  on.  The  danger  of 
ignition  of  the-  solvent  may  be  avoided  by  inserting  in  the  flask 
a  glass  tube,  extending  to  within  a  few  centimetres  of  the  level 
of  the  liquid,  supported  firmly  by  a  clamp,  and  attached  by  rubber 
tubing  to  the  suction.  The  tube  must  at  no  time  touch  the 
liquid. 

For  rapid  evaporation  of  small  quantities  of  ether,  the  following 
method  of  procedure  is  recommended  :  A  few  cubic  centimetres 
of  the  solution  are  placed  in  a  sufficiently  wide  test-tube  ;  this  is 
warmed,  with  continuous  shaking,  over  a  small,  luminous  flame. 


34 


GENERAL   PART 


After  the  first  portion  is  evaporated,  the  second  is  added,  and 
so  on.  Since  the  vapours  of  the  ether  almost  regularly  become 
ignited,  this  event  should  always  be  expected,  and  should  occasion 
no  alarm.  When  it  happens,  the  heating  is  interrupted  for  a 
moment,  and  the  flame  is  easily  extinguished  by  blowing  on  it  or 
covering  the  mouth  of  the  test-tube.  If  the  tube  is  held  as  nearly 
horizontal  as  possible  during  the  heating,  the  danger  of  ignition 
is  lessened. 

If  it  is  desired  to  distil  off  a  larger  quantity  of  ether,  ligrdin, 
or  carbon  disulphide,  and  to  recover  it  by  condensation,  the  re- 
ceiver is  attached  to  the  condenser  tube  by  a  cork,  and  the  flask 
is  heated  by  immersing  it  in  a  water-bath  containing  hot  water. 
To  prevent  the  liquid  from  being  superheated,  a  silk  thread  as 
frayed  as  possible  at  the  end  reaching  to  the  bottom  of  the  flask 
is  suspended  from  the  neck  and  the  flask  is  shaken  frequently 
during  the  distillation  (Fig.  28).  The  entire  quantity  of  the  liquid 
is  not  placed  in  the  flask  at  once,  but  only  a  portion  :  after  the 
solvent  has  been  distilled  off  from  this,  an- 
other portion  is  added,  and  so  on. 

By  the  use  of  the  so-called  safety  water- 
bath,  i.e.  one  in  which  the  flame  is  sur- 
rounded by  a  wire  gauze  as  in  Davy's  Safety 
Lamp,  ether  and  ligro'in  can  be  distilled  by 
continuous  heating  with  a  flame.  It  is  not 
safe  to  distil  off  carbon  disulphide  even  from 
this  apparatus,  since,  when  it  becomes  suffi- 
ciently hot,  it  will  ignite  spontaneously  with- 
out the  intervention  of  a  flame. 

By  the  use  of  a  coil  condenser  (Fig. 
27)  the  distillation  of  solvents  is  greatly 
facilitated.  The  free  flame,  if  it  be  sur- 
rounded by  a  cylinder  of  wire  gauze,  may 
be  employed  in  place  of  a  water-bath. 
A  piece  of  rubber  tubing  attached  to  the 
side  tube  of  the  receiver  carries  the  vapours  to  a  hood  or  below 
the  surface  of  the  table. 


FIG.  27. 


DISTILLATION 


35 


The  apparatus  best  adapted  to  distilling  off  any  desired  quan- 
tity of  ether  is  represented  in  Fig.  29.  A  fractionating  flask, 
into  the  neck  of  which  a  dropping-funnel  is  inserted,  is  con- 
nected with  an  ordinary  condenser  or  an  upright  coil  condenser. 
During  the  heating  by  means  of  hot  water,  or  in  special  cases, 
the  water-bath  may  be  heated  with  a  flame,  or  the  flask  may  be 
heated  directly  by  a  flame  protected  by  a  safety  gauze,  the  ethereal 
solution  is  allowed  to  flow  gradually  from  the  dropping-funnel  into 
the  flask  in  the  bottom  of  which  are  a  few  scraps  of  platinum, 
or  pieces  of  unglazed  porcelain. 


FIG.  28. 


If  the  flow  of  the  solution  is  regulated  so  that  the  same  quantity 
of  liquid  is  added  as  that  distilled,  the  operation  may  be  carried 
on  continuously,  for  hours.  The  quantity  of  ether  collected  in  the 
receiver  is  prevented  from  becoming  too  large,  by  pouring  it  into  a 
larger  vessel  from  time  to  time.  To  protect  the  ether  from  igni- 
tion, the  mouth  of  the  receiver  is  closed  by  a  loose  plug  of  cotton, 
or  the  receiver,  united  to  the  condensing  tube  by  a  cork,  is  con- 
nected with  the  hood  by  rubber  tubing.  Besides  its  convenient 
manipulation,  this  method  possesses  the  further  advantage  that 
after  the  ccmpletion  of  the  distillation  the  dropping-funnel  may 
be  replaced  by  a  thermometer,  and  the  residue  can  be  distilled 
directly  from  the  fractionating  flask.  This  is  an  especially  eco- 


36  GENERAL   PART 

nomical  procedure  when  the  quantity  of  the  dissolved  substance 
is  small.  In  a  case  of  this  kind  the  size  of  the  flask  is  selected 
with  reference  to  the  residue  that  may  be  expected.  In  distilling 
off  alcohol,  it  is  necessary  to  heat  the  water-bath  continuously, 
and  to  always  use  threads.  The  distillation  may  be  hastened  by 
placing  the  flask  not  upon,  but  in,  the  water-bath.  If  a  solution 
of  common  salt  is  employed  in  the  bath,  the  temperature  is  raised, 
and  the  distillation  proceeds  still  more  rapidly. 

Cylinders  that  fit  in  the  water-bath,  and  are  perforated  at  the 
bottom  and  on  the  sides,  may  be  used  with  great  advantage  in 
place  of  the  simple  ring  covers.  This  device  permits  the  heating 
of  the  distillation  flask  with  steam,  not  only  at  the  bottom,  but  also 
on  the  sides. 

If  one  has  had  sufficient  experience  in  laboratory  work,  alcohol 


FIG.  29. 

may  be  distilled  off  by  heating  the  flask  on  a  wire  gauze  or  sand- 
bath  over  a  flame.  In  this  case  especial  care  must  be  taken  not 
to  use  too  large  quantities  at  one  time.  Benzene  can  be  distilled 
off  under  the  same  conditions  as  alcohol.  The  methods  appli- 
cable to  high  boiling  liquids  have  been  given  under  "Distilla- 
tion." (See  page  16.) 


DISTILLATION   WITH    STEAM 


37 


In  comparatively  few  cases  the  difference  between  the  boiling- 
points  of  the  solvent  and  the  dissolved  substance  is  a  slight  one ; 
under  these  conditions  the  separation  must  be  effected  by  a 
systematic  fractional  distillation  with  the  aid  of  fractionating 
apparatus. 

DISTILLATION    WITH   STEAM 

A  particular  kind  of  distillation,  very  frequently  employed  in 
organic  work  for  the  purification  or  separation  of  a  mixture,  is 
distillation  with  steam.  Many  substances,  even  those  distilling  far 
above  ioo°,  or  those  not  volatile  without  decomposition,  possess 
the  property,  when  heated  with  water,  or  when  steam  is  passed 
over  or  through  them,  of  volatilising  with  the  steam.  This  phe- 
nomenon is  explained  as  follows :  Suppose  we  take  a  mixture  of 
two  liquids  that  are  absolutely  insoluble  in  one  another.  Each 
liquid  will  exert  its  own  vapour  pressure  as  it  would  if  it  were 
alone,  and  will  not  in  any  way  be  influenced  by  the  other.  A 
practical  example  of  this,  to  be  taken  up  later,  is  a  mixture  of 
water  (B.  P.  100°)  and  brombenzene  (B.  P.  155°).  When  this  is 
gradually  heated,  the  vapour  pressure  of  both  substances  will  in- 
crease, and  boiling  will  begin  when  the  sum  of  the  vapour  pres- 
sures is  equal  to  the  barometric  pressure,  which  we  shall  assume 
to  be  760  mm.  The  mixture  will  boil  at  95.25°,  as  will  be  seen 
from  the  following  table  : 


t 

Vapour  pressure  1  of  CcH.-,Br 

Vapour  pressure  of  H2O 

Total 

95° 

120  mm. 

634  mm. 

754  mm. 

95.25° 

121  mm. 

639  mm. 

760  mm. 

96° 

124  mm. 

657  mm. 

781  mm. 

Thus  at  this  temperature  a  mixture  of  water  and  brombenzene 
distils  over.  The  proportion  of  the  two  substances  will  be  seen 
from  the  following  considerations  :  According  to  Avogadro's  Law, 

1  The  vapour  pressure  of  brombenzene  is  calculated  by  interpolation  from  the 
values  found  by  Young  at  90°  and  100°.  (Journ.  Chem.  Soc.  55,  p.  486.) 


38  GENERAL   PART 

under  the  same  conditions  of  temperature  and  pressure  equal 
volumes  of  all  ideal  gases  contain  the  same  number  of  molecules. 
If  temperature  is  the  same  and  pressure  different,  the  number  of 
molecules  in  the  same  volume  will  be  proportional  to  the  pressure. 
Let  us  now  consider  the  mixture  consisting  of  the  vapours  of  water 
and  brombenzene  at  95.25°.  Since  at  this  temperature  the  former 
exerts  a  vapour  pressure  of  639  mm.,  and  the  latter  a  vapour  pres- 
sure of  121  mm.,  the  molecular  quantities  must  be  in  the  same 
ratio,  i.e.  for  every  639  molecules  of  water  121  molecules  of  brom- 
benzene will  be  present.  In  order  to  calculate  the  weights  of  the 
substances  that  distil  over,  we  must  multiply  the  number  of  mole- 
cules with  the  molecular  weight  of  each  substance.  In  our 
example,  for  639  x  18  parts  by  weight  of  water,  121  x  157  parts 
by  weight  of  brombenzene  will  distil  over,  which  corresponds 
approximately  to  3  parts  by  weight  of  water  and  5  parts  by  weight 
of  brombenzene.  This  proportion  remains  constant  until  one  of 
the  two  has  completely  distilled  over. 

It  must  be  stated  that  such  an  ideal  condition  of  distillation 
with  steam  is  never  realised.  There  are  no  substances  that  are 
absolutely  insoluble  in  one  another.  Furthermore,  there  is  the 
disturbing  influence  of  vapour  pressure,  which  is  quite  small  in  the 
example  given  above.  And  again,  since  vapours  do  not  strictly 
obey  Avogadro's  Law,  the  ratio  of  the  two  substances  in  the  dis- 
tillate is  somewhat  irregular.  Finally,  since  the  heating  is  carried 
out  by  steam,  and  the  temperature  of  the  substance  is  never  raised 
to  the  exact  boiling  point,  the  mean  temperature  is  somewhat 
different  from  that  given  above,  and  the  proportions  are  therefore 
altered. 

Apparatus.  —  The  apparatus  used  for  distillation  with  steam 
is  represented  in  Fig.  30.  A  round  flask  inclined  at  an  angle 
is  closed  by  a  two-hole  cork;  through  one  hole  passes  a  not 
too  narrow  glass  tube  reaching  to  the  bottom  and  serving  to 
lead  in  the  steam;  the  other  hole  bears  a  short  glass  tube 
the  end  of  which  is  just  below  the  cork,  the  other  end  is  con- 
nected with  a  long  condenser.  The  distillation  flask  selected  is 
of  such  a  size  that  the  liquid  fills  it  not  more  than  half  full. 


DISTILLATION   WITH   STEAM  39 

In  order  that  the  steam  may  act  on  an  oil  at  the  bottom  of 
the  flask,  the  inlet  tube  is  bent  so  that  it  may  reach  the  lowest 
point  of  the  flask.  Steam  is  generated  in  a  tin  vessel  about 
half-filled  with  water,  the  neck  being  closed  by  a  two-hole  stop- 
per ;  into  one  hole  is  inserted  a  safety-tube  partially  filled  with 
mercury ;  the  lower  end  of  this  tube  does  not  touch  the  water ; 
through  the  other  hole  passes  the  outlet  tube  bent  at  a  right 
angle. 

Method  of  Procedure.  —  The  experiment  is  begun  by  heating 
the  steam  generator  and  the  flask  simultaneously,  the  former  con- 
veniently by  means  of  a  low  burner  (Fletcher  burner).  The  flask 
may  be  heated  on  a  wire  gauze  over  a  free  flame ;  but  since  at 
times  a  very  troublesome  "  bumping  "  will  occur,  it  is  better,  if 
this  happens,  to  heat  on  a  briskly  boiling  water-bath.  As  soon 
as  the  water  in  the  generator  boils  and  the  liquid  in  the  flask  has 
been  heated  to  the  proper  point,  the  tubes  of  the  two  vessels  are 
connected  with  rubber  tubing.  The  distillation  is  then  continued 
until  the  condensed  steam  passes  over  unaccompanied  by  any  of 
the  substance.  Should  the  steam  escape  from  the  safety-tube, 
the  generator  is  being  heated  too  strongly,  and  the  flame  should 
be  lowered.  To  prevent  the  partial  condensation  of  vapours  in 
the  upper  cool  part  of  the  flask  this  should  be  covered  with  sev- 
eral layers  of  thick  cloth  to  lessen  the  radiation  of  heat.  If  the 
quantity  of  substance  to  be  distilled  is  small,  so  that  only  a  small 
flask  need  be  used,  the  preliminary  and  continued  heating  of  the 
latter  is  superfluous :  the  steam  can  be  passed  at  once  into  the 
cold  liquid.  If  a  compound  is  very  easily  volatile  with  steam, 
the  introduction  of  the  latter  may  be  omitted  ;  in  this  case  it  is 
only  necessary  to  mix  the  compound  with  several  times  its  volume 
of  water  and  distil  directly  from  the  flask.  If  the  substance  to 
be  distilled  is  solid,  and  its  vapour  forms  crystals  in  the  condenser, 
these  may  be  removed  provided  the  substance  melts  below  100°, 
by  drawing  off  the  water  in  the  condenser  for  a  short  time.  The 
substance  is  melted  by  the  hot  steam  and  flows  into  the  receiver. 
If  after  this  operation  the  water  is  to  be  turned  into  the  condenser 
again,  it  must  be  done  slowly  at  first,  otherwise  the  cold  water 


4o 


GENERAL   PART 


DISTILLATION   WITH   STEAM  4! 

coming  in  contact  with  the  hot  condenser  may  easily  crack  it. 
When  the  melting-point  of  the  substance  is  above  100°,  in  order 
to  keep  the  condenser  free  from  crystals,  the  distillation  is  inter- 
rupted for  a  short  time,  and  the  crystals  are  pushed  out  of  the 
tube  by  a  long  glass  rod. 

The  end  of  the  operation  is  indicated,  if  the  substance  is  diffi- 
cultly soluble  in  water,  by  the  fact  that  the  water  passing  over 
carries  no  drops  of  oil  or  crystals  with  it.  But  when  the  substance 
*  is  soluble,  even  though  the  condensed  water  is  apparently  pure,  it 
may  still  contain  considerable  quantities  of  the  dissolved  substance. 
In  this  case,  to  determine  when  the  end  of  the  operation  has  been 


FIG.  31. 

reached,  a  small  quantity,  about  10  c.c.,  is  collected  in  a  test-tube, 
shaken  up  with  ether,  the  ether  decanted  and  evaporated.  If  no 
residue  remains,  the  distillation  is  finished.  When  a  substance 
shows  a  colour  reaction,  e.g.  aniline  with  bleaching  powder, 
advantage  is  taken  of  this  to  decide  the  question.  After  the 
distillation  is  ended  the  rubber  tubing  is  first  removed  from  the 
distilling  flask,  and  then,  after  this  has  been  done,  the  flame  under 
the  generator  is  extinguished.  This  point  is  also  carefully  ob- 
served when  the  distillation  is  interrupted ;  otherwise  it  may 
happen  that  the  contents  of  the  flask  will  be  drawn  back  into 
the  generator. 

Superheated  Steam.  —  In  dealing  with  very  difficultly  volatile 
compounds,  it  is  frequently  necessary  to  conduct  the  distillation 


42  GENERAL   PART 

with  the  aid  of  superheated  steam.  A  conically  wound  copper 
tube  is  interposed  between  the  steam  generator  and  the  distilling 
flask  (Fig.  31).  In  order  to  superheat  the  steam,  a  large  burner  is 
placed  under  the  spiral  in  such  a  position  that  the  flame  comes  in 
contact  with  the  interior  of  the  spiral.  Since  for  many  purposes 
it  is  necessary  to  use  superheated  steam  at  a  definite  temperature, 
a  small  opening  is  made  in  the  steam  exit  and  a  piece  of  metal 
tubing  affixed  to  it.  A  thermometer  is  inserted  into  this  tubulure 
and  held  in  position  by  means  of  asbestos  twine.  The  distillation 
is  still  further  facilitated  by  heating  the  flask  to  a  high  tempera- 
ture in  an  oil-  or  water-bath.  Under  these  conditions  the  sub- 
stance to  be  distilled  is  not  covered  with  a  layer  of  water. 

The  apparatus    represented   in    Fig.    31  A   was   proposed    by 
V.  Haehl  and  Co.  of  Strassburg.     It  is  made  in  different  sizes, 


=y 


FIG.  31  A. 

and  may  be  used  with  great  advantage  in  the  laboratory  and  for 
work  on  the  large  scale.  It  consists  of  a  hollow  filter-plate,  sur- 
rounded with  a  double  layer  of  thick  asbestos  board.  The  latter 
is  provided  with  a  large  opening  in  the  lower  half  for  the  heat  of 
the  flame.  A  number  of  smaller  openings  are  found  in  the  upper 
half,  which  permit  the  escape  of  the  hot  gases.  The  superheat- 
ing of  the  steam  is  rendered  very  efficient  by  the  passage  of  the 
hot  gases  through  the  numerous  canals. 


SEPARATION   OF   LIQUID   MIXTURES  43 


SEPARATION    OF    LIQUID    MIXTURES.      SEPARATION 
BY   EXTRACTION.      SALTING   OUT 

Separation  of  Liquids.  —  If  the  separation  of  large  quantities  ot 
two  non-miscible  liquids,  one  of  which  is  for  the  most  part  water 
or  a  water  solution,  is  to  be  effected,  it  can  be  done 
with  a  separating  funnel  (Fig.  32).  If  the  liquid 
desired  is  of  a  greater  specific  gravity  than  that  of 
water,  it  is  allowed  to  flow  off  through  the  stem  by 
opening  the  cock.  If,  however,  it  floats  upon  the 
water,  the  latter  is  first  allowed  to  flow  off,  and  the 
liquid  remaining  is  poured  out  of  the  top  of  the  fun- 
nel. By  this  manipulation  the  liquid  is  prevented 
from  coming  in  contact  with  the  portion  of  water 
remaining  in  the  cock,  and  adhering  to  the  sides  of 
the  stem.  For  the  separation  of  small  quantities  of 
liquids  a  small  separating  funnel,  the  so-called  drop- 
ping funnel,  is  employed.  If  the  quantity  of  liquid  is 
so  small  that  even  a  dropping  funnel  is  too  large,  a  FIG-  32- 
capillary  pipette  is  used  (Figs.  33  and  34).  The  mixture  to  be 
separated  is  placed  in  a  narrow  test-tube,  the  pipette  is  immersed 
in  the  mixture  almost  to  the  surface  of  contact  of  the  two  liquids 
in  case  the  upper  layer  is  to  be  removed,  the  test-tube  is  brought 
to  the  level  of  the  eyes,  and  the  upper  layer  drawn  off.  The 
tubing  is  then  closed  by  pressure  with  the  teeth  or  fingers  and  the 
pipette  removed  from  the  tube.  If  the  lower  layer  is  the  one 
desired,  the  pipette  is  immersed  to  the  bottom  of  the  test-tube, 
and  the  operation  conducted  as  before.  Pipettes  of  this  kind  are 
very  easily -made  from  glass  tubing;  and  if  one  is  accustomed  to 
work  with  them,  are  indispensable. 

Separation  by  Extraction.  —  When  a  substance  is  held  in  sus- 
pension or  dissolved  in  a  liquid,  generally  water,  the  removal  of 
the  dissolved  substance  may  be  effected  by  agitating  the  solution 
with  another  solvent  which  will  more  readily  dissolve  the  substance, 
but  which  is  not  miscible  with  the  first  liquid,  drawing  off  this  and 


44  GENERAL   PART 

distilling  it.  For  extraction,  ether  is  generally  used ;  in  special 
cases  carbon  disulphide,  ligroi'n,  chloroform,  benzene,  amyl  alco- 
hol, etc.,  may  be  used.  In  the  discussion  following  it  will  be 
assumed  that  the  extraction  is  made  with  ether. 

If  the  liquid  to  be  separated  is  insoluble  in  water  and  is  present 
in  such  a  small  quantity  that  a  direct  separation  would  cause  a 
loss  owing  to  the  adhesion  of  the  liquid  to  the  walls  of  the  vessel, 
or  if  it  is  held  in  suspension  by  the  water  in  the  form  of  individual 


FIG.  33.  FIG.  34. 

drops,  ether  is  added  to  the  mixture ;  it  is  then  shaken,  allowed 
to  stand,  the  two  layers  separated,  and  the  ether  evaporated. 

A  similar  method  is  followed  if  the  substance  is  completely 
soluble  in  water,  or  if  a  portion  of  it  is  soluble  and  the 
remainder  held  in  suspension.  If  from  an  aqueous  solution  a 
considerable  portion  of  a  solid  or  liquid  separates  out,  it  is  not 
immediately  extracted  with  ether,  but  if  the  substance  sepa- 
rating out  is  a  solid,  it  is  first  filtered  off;  if  a  liquid,  the  oily 
layer  is  separated  in  a  dropping  funnel,  and  then  the  filtrate  is 


SEPARATION  BY   EXTRACTION  45 

extracted  with  ether.  In  many  cases,  e.g.  when  the  layer  of  oil 
is  very  turbid,  or  the  solution  strongly  acid  or  alkaline,  thus 
rendering  filtration  difficult,  the  entire  solution  may  be  treated 
at  once  with  ether.  With  substances  soluble  in  water  the  extrac- 
tion must  be  repeated  one  or  more  times  in  proportion  to  the 
greater  or  less  solubility  of  the  substance.  If  it  is  desirable  to  avoid 
using  large  quantities  of  ether,  after  the  first  extraction  it  is  dis- 
tilled off  and  used  for  the  second  extraction,  and  so  on.  The 
extraction  is  repeated  until  a  test  portion  of  the  ethereal  solution, 
evaporated  on  a  watch-glass,  leaves  no  residue.  If  the  test  portion 
is  evaporated  by  blowing  the  breath  on  it,  the  beginner  will  prob- 
ably often  be  deceived  by  the  appearance  of  an  abundant  quan- 
tity of  crystals  of  ice,  formed  by  the  condensation  of  the  moisture 
of  the  breath,  due  to  the  cold  produced  by  the  evaporation  of  the 
ether.  Another  error  into  which  the  beginner  often  falls  when 
extracting  with  ether  is  this :  in  most  chemical  processes  small 
quantities  of  coloured  impurities  are  formed  ;  on  extraction,  these 
impart  a  colour  to  the  ether.  The  tendency  is  to  continue  the  ex- 
traction until  the  ether  is  no  longer  coloured ;  but  the  proper  method 
of  procedure  is  just  the  reverse  of  this.  On  extracting  colourless 
compounds,  the  colouring  of  the  ether  does  not  show  that  it  still 
contains  any  of  the  substance  dissolved;  the  above-mentioned  test 
gives  the  only  safe  indication  of  the  presence  of  the  substance. 

In  an  extraction  the  following  points  are  to  be  observed :  Hot 
liquids  are  allowed  to  stand  until  they  are  cold  before  they  are  ex- 
tracted with  ether,  carbon  disulphide,  or  other  low  boiling  solvents. 
It  frequently  happens  that,  after  long  standing,  two  layers  of  liquids 
will  not  separate,  in  consequence  of  the  formation  of  a  flocculent 
precipitate  floating  in  the  liquids  at  the  surface  of  contact.  This 
difficulty  may  be  obviated  either  by  stirring  the  liquids  with  a  glass 
rod,  or  by  giving  the  separating  funnel  a  circular  motion  in  a  hori- 
zontal plane,  in  such  a  way  as  not  to  cause  the  two  layers  to  be 
mixed  by  the  shaking.  Under  certain  conditions  the  neck  of  the 
funnel  may  be  closed  with  a  cork  bearing  a  glass  tube  attached  to 
the  suction  ;  by  this  means  the  space  over  the  liquid  is  exhausted. 
The  bubbles  of  gas  which  now  rise  through  the  liquid  frequently 


46  GENERAL  PART 

destroy  the  troublesome  emulsion.  The  same  object  may  also  be 
attained  by  adding  a  few  drops  of  alcohol  to  the  ether.  If  the  sepa- 
ration of  the  layers  is  very  imperfect,  the  cause  is  often  due  to  the 
fact  that  an  insufficient  quantity  of  ether  has  been  used ;  in  this  case 
more  ether  is  added.  If  all  of  these  methods  prove  ineffectual,  then 
a  complete  separation  may  be  obtained  by  first  filtering  the  mix- 
ture, best  with  the  aid  of  a  Biichner  funnel,  which  will  retain  the 
precipitate  causing  the  emulsion,  and  then  allowing  it  to  stand. 

Occasionally  when  extracting  an  aqueous  solution  containing 
inorganic  salts  with  ether,  they  will  separate  out  as  solids.  In 
this  case  water  is  added  until  the  salts  are  redissolved,  or  the 
solution  is  filtered,  with  suction. 

If  the  specific  gravity  of  an  ethereal  solution  is  approximately  the 
same  as  that  of  the  water  solution,  the  separation  often  takes  place 
only  with  difficulty.  Some  common  salt  is  then  added,  by  which 
the  specific  gravity  of  the  aqueous  solution  is  increased. 

Under  certain  conditions  both  the  ethereal  and  aqueous  solu- 
tions are  so  coloured  that  they  cannot  be  distinguished.  In  this 
case  the  separating  funnel  is  held  toward  the  light ;  in  the  even- 
ing a  luminous  flame  is  placed  behind  it,  and  the  eye  is  directed 
to  the  liquid  at  a  point  just  above  the  cock.  On  opening  the 
cock,  the  eye  will  readily  detect  the  layer  separating  the  two 
liquids,  as  it  approaches  the  opening. 

Theory  of  Separation  by  Extraction.  —  Suppose  we  take  a  mix- 
ture of  two  immiscible  solvents  i.  and  2.,  and  add  to  this  a  sub- 
stance that  has  the  same  molecular  weight  in  both  liquids,  and  is 
furthermore  twice  as  soluble  in  i.  as  in  an  equal  volume  of  2.  If 
we  use  a  quantity  of  the  substance  that  will  saturate  both  solvents, 
then  in  a  unit  volume  of  i.  we  shall  have  twice  as  much  in  solution 
as  we  have  in  a  unit  volume  of  2.,  and  the  concentrations  will  be 
in  the  ratio  of  2  :  i.  If  to  both  solvents  in  a  vessel  we  add  a 
quantity  of  the  substance  that  will  only  form  an  unsaturated  solu- 
tion, or  if  we  dissolve  the  substance  in  one  solvent  and  shake  this 
with  the  second  solvent,  we  shall  find  that,  in  either  case,  the  sub- 
stance distributes  itself  in  such  a  way  that  the  ratio  of  the  concen- 
trations (the  distribution  coefficient  /£)  is  again  2  :  i  (Berthelot  and 


SEPARATION  BY  EXTRACTION 


47 


Jungfleisch).  Suppose  we  represent  the  maximum  concentrations 
by  ^  and  K^  and  let  k±  and  k.2  represent  the  concentrations  of 
the  unsaturated  solutions.  We  have  the  equation  : 

k  =  — *  =  ^  - 
K%     £2 

If,  for  example,  the  amount  of  the  dissolved  substance  is  a,  and 
if  equal  volumes  of  solvents  i.  and  2.  are  taken,  after  the  first  ex- 
traction solvent  i.  will  contain  f  a,  while  solvent  2.  will  only  con- 
tain ^  a.  The  greater  the  difference  in  solubility  the  more  com- 
plete will  the  extraction  be.  When  two  volumes  of  i.  and  one 
volume  of  2.  are  used  for  extraction,  the  amount  of  a  in  two  vol- 
umes of  i.  may  be  calculated  in  the  following  manner : 


Solvent. 

Volumes. 

Dissolved 
Substance. 

Concentration,  i.e.  quotient  of 
dissolved  substance  and  volumes 
of  solvents. 

X 

I. 

2 

X 

2 

2. 

I 

a  —  x 

(«-*) 

The  ratio  of  concentrations  must  now  be  equal  to  the  distribution 
coefficient,  i.e.  : 

x 

2  2  4 

-, 7  =  - ,  and  hence  x  —  -  a. 

(a-x)      i'  5 

The  principle   of  distribution   may  be  generally  expressed  as 
bllows  : 


Solvent. 

Volumes. 

Dissolved 
substance. 

Concentration. 

Coefficient  of  dis- 
tribution of  i. 
according  to  2. 

X 

'• 

Vl 

X 

a  -  x 

* 

*, 

v, 

48 


GENERAL   PART 


,        >  i 

—    K,  *      *At    7  • 


In  practical  work  we  have  this  question  to  consider  :  Is  it  expedi- 
ent to  carry  on  the  extraction  in  one  operation  by  a  given  volume  of 
the  solvent,  or  do  this  in  several  operations  by  the  use  of  small  por- 
tions of  the  solvent  ?  The  question  may  be  answered  as  follows  :  In 
the  example  under  consideration,  a  single  extraction  by  an  equal 
volume  of  i.  dissolved  f  a.  If  in  a  second  experiment  we  only 
use  a  half  volume  of  i.  then  x  parts  of  a  will  go  into  solution,  and 
x  will  be  smaller  than  |-  a.  The  portion  that  remains  in  solution 
in  2.  will  be  (a  —  x).  We  therefore  have  the  following  ratio  : 


Concentration,        i.e. 

Solvent. 

Volumes. 

Dissolved  substance. 

quotient  of  dissolved 
substance   and  vol- 

umes of  solvents. 

I. 

I 
2 

X 

X 
-  —  2.X 
I 

2 

2. 

I 

a  -  x 

a  —  x 

But  the  ratio  of  concentrations  must  be  equal  to  the  coefficient 
of  distribution  ;  consequently  : 

2X  2  a 

—  =  - ;  or  x  —  -  • 

a  —  x      i  2 

One  half  of  a  is  therefore  in  solvent  i.  and  the  other  half  remains 
in  solvent  2.     If  we  now  shake  2.  with  the  second  half  of  solvent 

i.,  a  portion  equal  to  one  half  of  -,  namely  -,  will  be  extracted 


by  the  latter.     The  total  amount  extracted  by  using  solvent  i.  in 

a  &  -7 
two  portions  is  -  +  -  =  ^  a,  whereas  the  amount  extracted  when 

2  4  4 
the  solvent  is  used  in  one  operation  is  -|  a.  Thus  a  given  quantity 


SEPARATION   BY   EXTRACTION  49 

of  the  solvent  is  much  more  efficient  when  it  is  used  in  small 
portions  than  it  is  when  all  of  it  is  used  in  one  operation.  The 
first  procedure  has  the  disadvantage  of  requiring  more  time  than 
the  second.  But  since  in  laboratory  work  time  is  of  greater  con- 
sequence than  the  price  of  the  solvent,  large  quantities  of  the 
solvent  are  used  in  one  operation.  —  It  is  clear  from  these  obser- 
vations that  a  quantitative  extraction,  in  the  strict  sense  of  the 
word,  is  impossible,  even  by  a  repetition  of  the  process.  Thus 

--!--'+  «  +-?•••  cannot  possibly  be  equal  to  a. 
2      4      8      16 

The  above  discussions  apply  to  solvents  only  which  are  not 
themselves  miscible.  This  is  not  strictly  true  for  mixtures  of 
water  and  ether,  since  ether  is  soluble  in  water,  as  water  is  in  ether. 

The  same  formulas  may  be  used  to  express  the  solubilities  of 
unit  weights,  as  well  as  of  unit  volumes  of  solvents.  In  each  case 
the  distribution  coefficient  will  naturally  have  a  different  value. 

Salting  Out.  —  A  very  valuable  method  to  induce  substances 
dissolved  in  water  to  separate  out  is  known  as  "  salting  out." 
Many  substances  soluble  in  pure  water  are  insoluble  or  difficultly 
soluble  in  an  aqueous  solution  of  certain  salts  ;  if,  therefore,  sodium 
chloride,  potassium  chloride,  potash,  calcium  chloride,  ammonium 
chloride,  Glauber's  salt,  sodium  acetate,  ammonium  sulphate,  or 
other  salt  is  added  to  the  solution,  this  is  dissolved,  and  the  sub- 
stance previously  in  solution  separates  out.  By  this  method  many 
compounds  like  alcohol,  acetone,  etc.,  which  are  so  easily  soluble 
in  water  that  they  cannot  be  removed  from  it  by  extraction  with 
ether,  can  be  separated  out  with  ease.  The  method  of  procedure 
is  this  :  One  of  the  above-mentioned  salts,  usually  solid  potash,  is 
added  to  the  solution  until  no  more  will  dissolve.  The  substance 
thus  forced  out  of  solution  collects  above  the  heavier  salt-solution 
and  is  removed  by  decantation  or  suction. 

A  combination  of  extraction  and  salting  out  also  presents  many 
advantages.  If  to  the  solution  of  a  compound  in  water  one  of 
the  salts  mentioned  is  added  —  it  is  best  to  use  finely  pulverized 
sodium  chloride  —  before  the  extraction  with  ether,  this  latter  is 
greatly  facilitated  for  several  reasons.  In  the  first  place,  a  portion 
E 


50  GENERAL  PART 

of  the  dissolved  substance  will  separate  out,  due  to  the  "  salting 
out "  action ;  furthermore,  the  solubility  of  the  substance  in  the 
the  new  solvent  —  sodium  chloride  solution  —  will  be  diminished 
so  that  on  extracting,  a  larger  portion  is  dissolved  by  the  ether 
than  on  treating  the  solution  directly  with  it,  and  finally,  ether 
does  not  dissolve  so  readily  in  a  sodium  chloride  solution  as  in 
water,  so  that  the  volume  of  the  ethereal  solution  is  larger.  The 
amount  of  sodium  chloride  to  be  added  is  about  25-30  grammes 
of  the  finely  pulverised  salt  to  100  c.c.  of  the  aqueous  solution. 
Unfortunately  the  method  of  "  salting  out "  has  not  been  so 
generally  adopted  in  scientific  laboratories  as  it  deserves,  while  in 
the  laboratories  of  technical  chemists  it  has  long  been  in  daily 
use.  Among  the  reagents  constantly  used,  a  bottle  of  solid  sodium 
chloride  should  not  be  wanting.  In  many  cases,  instead  of  the 
salt,  a  concentrated  aqueous  solution  may  also  be  used.  Con- 
cerning the  salting  out  of  electrolytes  see  theoretical  considera- 
tions under  "  Benzenesulphonic  Acid." 

DECOLOURISING.     REMOVAL   OF  TARRY   MATTER 

As  is  well  known,  animal  charcoal  possesses  the  property  of 
being  able  to  remove  the  colour  from  certain  solutions ;  for  this 
reason  it  is  frequently  employed  in  the  laboratory  to  free  a  colour- 
less substance  from  coloured  impurities.  If  it  is  to  be  used  to 
remove  the  colour  of  a  solid  substance,  the  latter  is  first  dissolved 
in  a  suitable  solvent,  then  boiled  with  the  animal  charcoal  and 
filtered.  Before  treating  a  hot  solution,  it  is  allowed  to  cool 
somewhat,  since  when  animal  charcoal  comes  in  contact  with 
liquids  heated  nearly  to  the  boiling-point,  a  violent  ebullition  is 
frequently  caused,  and  an  overflowing  of  the  liquid  may  easily  take 
place.  When  a  solvent  not  miscible  with  water  is  used,  the  ani- 
mal charcoal,  which  is  generally  moist,  is  previously  dried  on  the 
water-bath.  The  solvent  selected  is  such  that  upon  cooling  the 
decolourised  solution,  the  substance  will  crystallise  out.  In  carry- 
ing out  this  operation,  the  general  rule  that  no  animal  charcoal  is 
added  until  the  substance  to  be  decolourised  has  completely  dis- 


DECOLOURISING.     REMOVAL  OF  TARRY  MATTER          5 1 

solved,  should  be  followed.  Under  these  conditions  only,  is  it 
certain  that  a  portion  of  the  substance  does  not  remain  undissolved 
mixed  with  the  charcoal.  The  quantity  of  animal  charcoal  to  be 
added  to  a  solution  depends  upon  the  intensity  of  the  colour  of 
the  latter.  To  a  solution  very  slightly  coloured,  a  small  quantity 
is  added  ;  to  a  deeply  coloured  solution,  a  larger  quantity.  Very 
finely  divided  precipitates  in  water  which  pass  through  the  filter 
may  also  be  removed  by  the  use  of  animal  charcoal.  When,  e.g. 
tin  is  precipitated  with  hydrogen  sulphide,  the  tin  sulphide  is 
often  so  finely  divided  that  it  runs  through  the  filter.  If  the 
liquid  is  boiled  with  animal  charcoal,  the  filtration  presents  no 
difficulty. 

The  use  of  animal  charcoal,  especially  when  it  is  in  a  very  finely 
divided  condition,  has  the  disadvantage  that  at  times  it  passes 
through  the  filter  and  contaminates  the  filtrate.  This  may  be 
prevented  frequently,  by  filtering  again,  or  by  boiling  the  filtrate 
a  few  minutes  before  the  second  filtration.  When  substances  to 
be  analysed  have  been  decolourised  with  animal  charcoal,  care 
must  always  be  taken  to  prevent  the  contamination  of  the  sub- 
stance. In  such  cases  it  is  again  crystallised  without  the  use  of 
animal  charcoal.  This  difficulty  may  also  be  prevented  or  essen- 
tially lessened,  by  washing  the  charcoal  with  water  several  times 
before  using  ;  the  portion  suspended  in  the  water  is  decanted,  and 
only  the  coarser  residue  which  easily  settles  at  the  bottom  is  used. 

Recently  the  use  of  animal  charcoal  in  the  sugar  industry  has 
been  replaced  in  part  by  a  mixture  of  fine  wood  meal  and  floated 
infusorial  earth  (kieselguhr) .  This  mixture  ought  to  be  of  great 
advantage  in  the  laboratory,  for  decolourising  purposes,  if  used  in 
the  same  way  on  a  small  scale.  To  the  mixture  is  ascribed  very 
superior  purifying  properties,  so  that  by  using  much  smaller  quan- 
tities the  same  effect  is  obtained  as  with  far  larger  quantities  of 
animal  charcoal.  In  order  to  prevent  an  easily  oxidisable  liquid 
from  decomposing  when  it  is  heated  in  the  air  —  this  action  being 
generally  attended  with  more  or  less  colouration  —  a  gaseous  re- 
ducing or  protecting  agent  is  passed  through  it ;  e.g.  sulphur  dioxide, 
hydrogen  sulphide,  or  carbon  dioxide.  Very  easilv  oxidisable  sub- 


52  GENERAL  PART 

stances  are  not  evaporated  in  a  dish,  but  in  a  flask,  since  in  this 
the  liquid  is  better  protected  from  the  action  of  the  air. 

Not  only  coloured  impurities,  but  those  of  a  tarry  character, 
may  also  be  removed  by  boiling  with  animal  charcoal  as  above 
described.  A  mixture  of  wood  meal  and  infusorial  earth  with 
which  the  solution  may  likewise  be  boiled  is  said  to  be  of  great 
value. 

For  the  absorption  of  tarry  impurities,  in  so  far  as  they  are 
liquid  or  oily,  unglazed,  porous  plates  (drying  plates)  may  be 
used  with  advantage,  the  substances  being  firmly  pressed  out  with 
a  spatula  in  a  thin  layer.  If  one  pressing  out  is  insufficient,  the 
substance  is  spread  out  again  upon  a  fresh,  unused  portion  of 
the  plate.  The  absorption  of  an  oil  may  often  be  facilitated  by 
moistening  the  substance  on  the  plate  with  alcohol,  ether,  or 
ligroin,  which  at  times  will  dissolve  the  impurities  without  causing 
a  solution  of  the  substance.  Oily  by-products  may  also  be  removed 
by  pressing  the  substance  between  a  number  of  layers  of  filter- 
paper.  For  this  purpose  either  a  screw-press  is  used,  or  the 
substance  is  placed  in  layers  of  filter- paper  between  two  wooden 
blocks,  the  upper  one  of  which  bears  a  heavy  object. 

DRYING 

Drying  Solid  Compounds.  —  Under  the  chapter  on  "Crystallisa- 
tion," page  9,  the  method  of  drying  moist  crystals  has  already  been 
given.  This  method  is  naturally  applicable  to  all  solids,  even  if 
they  are  not  crystallised,  or  only  imperfectly  crystallised,  so  that  it 
will  be  unnecessary  to  repeat  the  directions  already  given.  But 
a  few  methods,  not  so  refined,  and  generally  employed  in  dealing 
with  crude  products  will  be  referred  to  here.  Before  a  substance 
is  dried  by  allowing  it  to  lie  in  the  air  or  in  a  desiccator,  or  by 
heating,  the  greatest  portion  of  the  moisture  is  removed  by  press- 
ure, as  follows :  The  substance  lying  between  a  number  of  layers 
of  filter-paper  is  placed  in  a  screw  press,  and  pressure  applied. 
The  operation  is  repeated,  and  the  paper  renewed,  until  it  is  no 
longer  moistened.  If  a  solid  is  not  contaminated  by  water  or  other 


DRYING 


53 


solvent,  but  by  a  liquid  by-product,  which  one  desires  to  obtain, 
the  paper,  after  it  has  absorbed  this  liquid  substance,  can  be  ex- 
tracted with  a  solvent,  like  ether.  Large  masses  of  a  compound 
•  not  too  finely  granulated  can  be  tied  up  in  a  piece  of  filter-cloth 
of  fine  texture,  placed  in  the  screw  press,  and  pressure  applied. 
Smaller  quantities  of  a  substance  may  be  pressed  out  between  two 
wooden  blocks,  the  upper  of  which  bears  a  heavy  object. 

Very  often  solids  may  be  dried  by  making  use  of  the  power 
of  unglazed  porcelain  to  absorb  liquids  with  avidity.  The  sub- 
stance to  be  dried  is  pressed  out  in  a  thin  layer  upon  a  suitable 
piece  of  an  unglazed  porcelain  plate,  with  a  spatula,  and  is  allowed 
to  stand  for  some  time,  longer  or  shorter,  as  may  be  necessary. 
If  one  pressing  out  is  not  sufficient,  the  operation  is  repeated, 
using  a  fresh  plate.  Oily  and  tarry  impurities  may  also  be  removed 
in  this  way,  as  mentioned  above. 

Compounds  which  fuse  without  decomposition  may  be  dried 
either  upon  the  water-bath  or  in  an  air-bath,  or  by  heating  over 
a  free  flame  until  they  melt,  allowing  them  to  solidify,  and  then 
pouring  off  the  water. 

In  order  to  dry  a  substance  at  a  high  temperature  in  a  vacuum, 
two  glass  hemispheres,  the  edges  of  which  are  ground  and  fitted 
together,  are  used.  The  upper  vessel  is  supplied  with  a  tubulure, 
the  opening  of  which  is  closed  by  a  cork  bearing  a  glass  tube  bent 
at  a  right  angle  connected  with  suction.  The  sphere  may  be 
heated  by  immersion  in  a  large  quantity  of  hot  water  or  on  a 
boiling  water-bath.  The  upper  hemisphere  is  enveloped  in  a 
cloth  to  prevent  the  condensation  of  the  vapours. 

Drying  Agents  for  Liquids.  —  Liquids  are  dried  (deprived  of 
water)  either  by  placing  in  them,  or  in  a  solution  of  them,  drying 
agents.  The  most  frequently  employed  drying  agents  are  : 

Calcium  chloride, 

(a)   granulated, 

(*)   fused, 

Potassium  hydroxide, 
Sodium  hydroxide, 


54  GENERAL  PART 

Ignited  potash, 

Fused  sodium  sulphate, 

Dehydrated  magnesium  sulphate. 

Less  frequently  used  are  :  lime,  barium  oxide,  anhydrous  sodium 
carbonate,  anhydrous  copper  sulphate,  phosphorus  pentoxide, 
sodium,  and  others. 

In  the  choice  of  a  drying  agent  care  must  be  taken  to  select 
one  which  will  not  react  with  the  substance  to  be  dried.  For 
example,  calcium  chloride  unites  to  form  double  compounds  with 
alcohols  as  well  as  with  bases.  Consequently,  for  drying  these 
two  classes  of  compounds,  calcium  chloride  is  never  used.  Caustic 
potash  and  caustic  soda,  as  is  well  known,  react  with  acids  and 
phenols  to  form  salts,  upon  alcohols  to  form  alcoholates,  and  upor 
esters,  saponifying  them.  These  drying  agents  are  never  used 
with  these  substances.  Further,  acids  are  never  dried  with  car- 
bonates, owing  to  the  salt  formation  taking  place. 

Calcium  chloride  is  employed  in  two  forms,  —  granulated  and 
fused.  The  former  acts  more  energetically,  since  it  possesses  a 
larger  acting  surface.  Still,  it  has  the  disadvantage  of  being  more 
porous  than  the  fused  variety  and  in  consequence  of  this  porosity 
the  loss  of  the  substance  being  dried  is  greater.  For  drying  small 
quantities  of  a  substance,  or  liquids  containing  very  little  moisture, 
it  is  better,  therefore,  to  use  fused  calcium  chloride. 

On  drying  bases  with  caustic  potash  or  caustic  soda,  it  must  be 
borne  in  mind  that  these  drying  agents  may  be  contaminated,  at 
times,  with  potassium  nitrite  or  sodium  nitrite.  Since  these  latter 
act  upon  bases,  decomposing  them,  it  is  necessary  to  use  the  pure 
alkalies,  or  in  place  of  them  potassium  carbonate  or  Glauber's  salt. 

Methods  of  Drying. —  As  already  mentioned,  liquids  may  be 
dried  either  in  the  undiluted  form  or  in  solution.  The  first  method 
is  followed  when  the  quantity  of  the  liquid  is  considerable,  so  that 
the  loss  of  the  substance  necessarily  incident  to  the  adhesion  of 
the  liquid  to  the  drying  agent  cannot  amount  to  a  large  percent- 
age of  the  whole.  Low  boiling  liquids  are  always  dried  directly, 
without  the  use  of  a  solvent.  If  a  "solution  of  a  higher  boiling 


METHODS  OF  DRYING  55 

compound  is  to  be  dried,  it  is  done  before  the  solvent  is  distilled 
off.  A  small  quantity  of  a  substance  or  a  viscous  substance  is 
designedly  treated  with  a  diluting  agent,  generally  ether,  and 
is  then  dried. 

The  drying  is  accomplished  by  placing  the  drying  agent  in  the 
liquid  and  allowing  the  two  substances  to  remain  in  contact  for 
a  longer  or  shorter  time,  according  to  circumstances.  So  long 
as  a  liquid  appears  turbid,  it  has  not  been  deprived  of  its  moisture. 
A  liquid  about  to  be  dried  must  never  contain  drops  of  water 
which  are  visible  ;  in  case  it  does,  it  must  be  treated  in  a  separating 
funnel  or  the  water  drawn  off  with  a  capillary  pipette :  it  is  then 
dried.  If  only  a  few  small  drops  of  water  are  present,  the  liquid 
is  first  filtered  through  a  small  folded  filter,  or  it  is  poured  care- 
fully into  another  vessel,  and  the  water  drops  will  remain  in  the 
first  vessel,  adhering  to  the  walls.  When  a  separation  of  an  ethereal 
from  an  aqueous  solution  is  to  be  made,  to  prevent  a  portion  of 
the  water  from  being  carried  along  with  the  ethereal  solution,  the 
former  is  not  drawn  off  through  the  cock  of  the  vessel,  but  is 
poured  out  of  the  mouth,  as  has  already  been  mentioned. 

If  a  liquid  contains  very  much  moisture,  and  this  is  the  case 
especially  in  turbid,  milky  liquids,  it  frequently  happens  that  the 
drying  agent  will  absorb  enough  water  to  dissolve  itself  and  thus 
form  an  aqueous  solution.  In  this  case  a  fresh  quantity  of  the 
drying  agent  is  not  added  at  once,  but  the  separation  of  the  two 
layers  is  effected  by  a  separating  funnel,  pipette,  or  by  decanting 
one  of  the  layers. 

A  similar  rule  obtains  for  undiluted  liquids.  The  drying  of 
high  boiling  substances,  if  they  are  not  volatile  at  the  temperature 
of  the  water-bath,  may  be  greatly  facilitated  by  heating  them  with 
the  drying  agent  on  the  water-bath. 

If  the  boiling  point  of  a  liquid  is  above  200°,  it  may  be  freed 
from  water,  without  the  aid  of  a  drying  agent,  by  heating  for  some 
time  on  a  water-bath  under  diminished  pressure.  The  water 
will  thus  distil  over.  The  apparatus  represented  in  Fig.  20, 
page  27  is  employed  for  this  purpose.  The  use  of  a  manometer 
will  be  unnecessary  if  this  is  connected  with  a  good  suction  pump. 


GENERAL   PART 


Before  distilling  a  liquid  which  has  been  dried,  or  before  dis- 
tilling off  the  solvent  from  such  a  liquid,  it  is  poured  off  from  the 
drying  agent.  To  obtain  the  small  portions  which  adhere  to  the 
latter  it  may  be  washed  with  a  small  quantity  of  the  dried  solvent. 
Low  boiling  individual  liquids  (boiling  on  water-bath)  can,  under 
certain  conditions,  be  distilled  without  a  previous  separation  from 
the  drying  agent.  If  the  liquid  to  be  dried  is  of  such  a  specific 
gravity  that  the  drying  agent  will  float  in  it,  then,  in  order  to  effect 
the  separation,  it  is  poured  through  a  funnel  containing  a  small 
quantity  of  glass  wool,  or  asbestos.  In  some  cases,  which,  how- 
ever, are  rare,  a  liquid  not  easily  volatile  may  be  dried  by  expos- 
ing it  in  a  dish  as  shallow  as  possible  in  a  partially  exhausted 
desiccator. 

FILTRATION 

While  in  analytical  operations  it  is  much  more  desirable  to 
conduct  filtrations  without  employing  pressure,  the  precipitates 
obtained  in  organic  preparation  work  are  filtered  with  pressure 
whenever  it  is  possible.  The  method  presents  a  number  of  ad- 
vantages :  the  filtration  may  be  made  in  a  much  shorter  time ;  the 
liquid  may  be  much  more  completely  sepa- 
rated from  the  precipitate,  in  consequence  of 
which  the  latter  will  dry  more  rapidly,  etc. 

The  student  has  already  learned  the  meth- 
ods of  filtering  without  pressure  in  the  opera- 
tions of  analytical  chemistry,  but  he  is  advised 
to  reread  the  chapter  on  Crystallisation  (see 
page  i). 

Filtration  with  Suction.  —  For  filtering  un- 
der pressure  (suction),  a  filtering  flask  a  (suc- 
tion flask)  with  a  side-tube  b  (Fig.  35)  is  used. 
An  ordinary  flask  may  be  converted  into  a 
suction  flask  by  fitting  to  it  a  two-hole  rubber 
stopper  ;  through  one  hole  is  passed  the  stem 
of  a  funnel,  through  the  other  a  glass  tube, 
bent  at  a  right  angle,  one  end  of  which  passes  just  through  the  cork, 


FILTRATION  5; 

while  the  other  is  attached  to  the  suction.  For  this  purpose  flasks 
with  thick  walls  are  selected,  in  order  that  they  may  not  be  crushed 
by  the  atmospheric  pressure  on  exhaustion ;  if  a  thin- walled  flask 
is  used,  it  must  be  exhausted  but  slightly. 

The  funnel  used  is,  in  many  cases,  the  ordinary  conical  glass  form, 
in  which  is  placed  the  filter.  If  the  funnel  is  imperfect  in  construc- 
tion, and  does  not  possess  the  correct  angle  (60°),  the  filter  is  made 
narrower  or  wider,  as  the  case  may  be,  to  accommodate  it  to  the 
angle  of  the  funnel.  In  order  that  the  point  of  the  filter  not  sup- 
ported by  the  glass  walls  of  the  funnel,  may  not  tear  on  exhaustion, 
a  platinum  cone  c  is  previously  placed  in  the  funnel. 

If  a  platinum  cone  is  not  at  hand,  it  may  be  replaced  by  a  coni- 
cally  folded  piece  of  parchment  paper  or  filter-cloth.  The  filter 
is  moistened  with  the  same  liquid  which  is  to  be  filtered,  otherwise 
it  may  happen  that  the  filtration  is  prevented,  or,  at  least,  rendered 
difficult ;  e.g.  if  the  filter  has  been  moistened  with  water,  and  an 
alcoholic  solution  is  to  be  filtered  through  it,  the  substance  dis- 
solved in  the  alcohol  may  be  precipitated  in  the  pores  of  the  filter 
by  the  water.  If  a  liquid  foams  excessively  on  filtering,  as  happens 
at  times  with  alkaline  liquids,  the  rubber  tubing  is  removed  sud- 
denly from  time  to  time  from  the  filter-flask.  The  pressure  of  the 
in-rushing  air  destroys  the  bubbles.  The  foaming  may  also  be  pre- 
vented at  times  by  treating  the  filtrate  with  a  few  drops  of  alcohol 
or  ether.  This  is  one  of  the  common  methods  of  preventing  foam- 
ing in  general.  When  filtering  very  small  quantities  of  a  liquid,  a 
test-tube  is  placed  in  the  filter-flask,  as  is  represented  in  Fig.  36. 

The  suction  surface  may  be  increased  by  placing  a  so-called 
filter-plate  of  'glass  or  porcelain  in  the  funnel  (Fig.  37).  If  a 
filter-plate  is  used,  the  filter-paper  should  be  of  two  thicknesses. 
Upon  the  plate  is  first  placed  a  round  filter  of  exactly  the  same 
size  as  the  plate,  and  upon  this  another  round  filter,  the  edge  of 
which  projects  about  2-3  mm.  beyond  that  of  the  plate. 

The  Blichner  funnel  is  indispensable  in  working  with  organic 
substances.  In  consequence  of  its  large  suction  surface,  a  very 
rapid  filtration  is  possible.  In  the  filtration  of  large  quantities 
of  substance  it  should  always  be  used  (Fig.  38). 


GENERAL  PART 


A  double  filter  (described  above)  may  be  used  in  this,  but  in 
most  cases  a  single  filter  is  sufficient.  Since  the  Biichner  funnels 
are  made  of  porcelain,  and  consequently  are  opaque,  they  must  be 
carefully  cleaned  immediately  after  using. 


FIG.  36. 


FIG.  37. 


FIG.  38. 


Similar  to  the  Biichner  funnel  in  its  construction  and  action  is 
the  so-called  "  Nutsch  "  filter.  This  consists  of  a  shallow  dish  with 
a  perforated  bottom,  which  is 
fitted  to  the  cover  of  a  tubu- 
lated cylinder  by  means  of  a 
rubber  ring,  the  joint  being 
air-tight  (Fig.  39). 

If  the  solution  to  be  filtered 
acts  on  the  filter-paper,  filter- 
cloth  may  be  used  in  its  place. 
A  fine  or  coarse  meshed  cloth 
is  selected,  according  to  the 
nature  of  the  precipitate  ;  it  is 
moistened  before  the  filtra- 
tion. 

If  this  is  also  attacked, 
nitrocellulose  cloth  may  be 
used ;  it  is  made  by  treating  FlG-  39- 

a  cloth  woven  from  plant  fibres  with  a  mixture  of  nitric  and  sul- 
phuric acids.    Concentrated  sulphuric  acid  may  be  filtered  through 


FILTRATION  59 

it.  Such  cloth  and  other  substances  containing  nitrocellulose  must 
always  be  preserved  under  water,  on  account  of  their  explosiveness. 
In  cases  of  this  kind  the  precipitate  is  retained  by  using  glass 
wool,  or  better,  long  fibrous  asbestos,  with  which  the  bottom  of  the 
funnel,  containing  in  this  case  a  platinum  cone,  is  filled,  or  it  is 
spread  out  in  thin  layers  over  a  filtering  plate,  or  on  the  surface  of 
a  Biichner  funnel.  Under  these  conditions,  the  suction  is  applied 
gently  at  the  beginning  of  the  filtration ;  as  soon  as  a  large  quantity 
of  the  precipitate  has  accumulated,  the  suction  is  increased.  Re- 
cently acid-  and  alkali-proof  filter  disks  have  also  been  used  in  the 
arts.  By  the  aid  of  asbestos  linings  these  may  be  placed  in  conical 
or  Biichner  funnels,  and  made  to  render  excellent  service.  Very 
coarse-grained  precipitates  can  be  filtered  without  the  use  of  a  filter 
by  placing  in  the  point  of  an  ordinary  glass  funnel  a  sphere  of  glass  (a 
marble)  ;  this  is  surrounded  by  glass  wool,  or  asbestos,  if  necessary. 
Pukall  Cells.  —  For  the  filtration  of  precipitates,  like  calcium 
sulphate,  barium  sulphate,  of  strongly  acid  liquids,  etc.,  PukalPs 

cells  (porous  cells),  made  of 
unglazed  clay,  are  very  use- 
ful. They  may  be  procured 
in  different  sizes  in  the  mar- 
ket, and  possess  either  the 
form  of  a  cylinder  or  a  mor- 
tar pestle.  The  operation  is 
performed  as  follows  :  In  the 

mouth  of  the  cell  is  placed  a 
FIG.  40. 

closely  fitting  stopper  bearing 

a  glass  tube  bent  twice  at  right  angles,  connected  with  a  filter-flask. 
The  tube  at  each  end  projects  slightly  below  the  stopper  (Fig.  40). 
The  cell  is  now  immersed  in  the  liquid  to  be  filtered,  contained  in 
a  beaker,  not  too  wide,  until  it  almost  touches  the  bottom.  When 
the  suction  is  applied,  the  liquid  filters  through  the  porous  walls 
until  the  cell  is  filled,  and  is  then  drawn  into  the  flask ;  the  pre- 
cipitate remains  behind  in  the  vessel,  and  for  the  most  part  is 
deposited  on  the  exterior  walls  of  the  cell. 

Filter-Press. —  For  the  filtration  of  large  quantities  of  substances 
which  filter  with  difficulty,  especially  dye-stuffs,  barium  sulphate, 


6o 


GENERAL   PART 


calcium  sulphate,  etc.,  fil- 
ter-presses are  often  used, 
of  which  the  Hempel  form 
will  be  described  (Fig.  41). 
The  separation  of  the  liquid 
from  the  precipitate  is  ef- 
fected in  the  cell  c,  which 
consists  of  two  perforated 
porcelain  plates  between 
which  is  a  rubber  ring.  The 
first  operation  in  working 
with  the  press  is  the  prepara- 
tion of  the  cells.  Two  circu- 
lar pieces  of  filter-cloth  and 
two  of  filter-paper  the  same 
size  as  the  plates  are  cut ; 
after  the  cloth  (linen  or 
muslin)  has  been  thoroughly 
moistened  with  water,  the 
cells  are  made  as  follows : 
At  the  bottom  comes  the 
perforated  plate  upon  which 
is  placed  one  layer  of  the 
filter-paper,  and  upon  this 
the  cloth.  After  a  wide  glass 
tube^-,  which  extends  almost 
to  the  opposite  side  of  the 
cell,  has  been  inserted  into 
the  opening  of  the  rubber 
ring,  this  is  placed  upon  the 
cloth,  then  follows  the  other 
piece  of  cloth,  filter-paper, 
and  finally  the  second  plate. 
The  cell  is  now  secured  by 
three  clamps,  one  of  which 
is  attached  near  the  glass 


FIG.  41. 


SEPARATION   OF  LIQUID    MIXTURES  6i 

tube,  and  the  others  equally  distant  from  this.  The  cell  is  now 
ready  for  the  nitration,  and  is  placed  between  the  two  corrugated 
glass  plates  d.  Before  it  is  connected  with  the  vertical  tube  b,  the 
pinch-cock  on  this  is  closed,  water  is  poured  into  the  funnel  a, 
and  the  cock  is  now  opened  until  the  vertical  tube  is  filled.  The 
cock  is  again  closed  and  the  tube  is  connected  with  the  cells,  the 
liquid  to  be  filtered  poured  into  the  funnel  and  the  cock  opened. 
During  the  resulting  filtration  care  is  taken  to  keep  the  funnel 
partially  filled  so  that  the  vertical  tube  is  constantly  full.  If  the 
first  portions  run  through  turbid,  they  are  returned  to  the  funnel. 
In  order  to  wash  the  precipitate  collecting  in  the  cell,  the  glass 
tube  passing  through  the  rubber  ring  is  partly  withdrawn,  so  that 
it  projects  into  the  cell  but  a  few  centimetres.  This  causes  a 
canal  to  be  formed  in  the  cell  from  which  the  wash  water  can 
permeate  the  precipitate  in  all  directions.  If  the  precipitate  is 
large  enough  to  completely  fill  the  interior  space  of  the  cell,  it 
forms  a  solid  cake  that  can  be  removed  without  difficulty.  But 
if  the  precipitate  is  small,  and  it  is  desired  to  obtain  it,  the  glass 
tube  is  withdrawn  from  the  rubber  ring,  the  contents  of  the  cell, 

generally  half-fluid,  are 
poured  into  a  beaker, 
the  cell  taken  apart,  and 
the  precipitate  adhering 
to  the  sides  scraped  off 
with  a  spatula.  By  fil- 
tering with  suction  a 
complete  separation  of 
the  liquid  and  precipi- 
FIG.  42.  tate  is  effected.  If  it  is 

desired  to  filter  larger  quantities  of  a  precipitate  than  can  con- 
veniently be  done  in  a  single  cell,  two  cells  connected  by  a  Y-tube 
may  be  used. 

Filtering  through  Muslin.  —  Precipitates  which  are  not  too 
finely  divided  may  be  filtered  off  through  a  filter-cloth  (muslin) 
stretched  over  a  wooden  frame  (filter-frame)  (Fig.  42).  A  square 
piece  of  muslin  or  linen,  after  being  thoroughly  moistened,  is 


62  GENERAL  PART 

fastened  on  the  four  nails  of  the  frame  in  such  a  way  as  to  cause 
a  shallow  bag  in  the  middle.  The  frame  is  placed  over  a  dish  oi 
the  proper  size  and  the  liquid  to  be  filtered  is  poured  on  the 
cloth  and  generally  filters  rapidly  through  it.  If  it  is  desired  after 
washing  the  precipitate  to  press  it  out,  the  cloth  is  taken  from 
the  four  corners,  folded  together,  and  squeezed  with  the  hands. 
The  precipitate  may  be  further  dried,  by  tying  up  the  opening 
of  the  bag  with  twine,  and  then  pressing  it  out  carefully  under  a 
screw-press. 


HEATING   UNDER   PRESSURE  63 


HEATING  UNDER   PRESSURE 

Sealed  Tubes.  Method  of  Filling.  —  If  it  is  desired  to  induce 
a  reaction  between  two  substances  at  a  temperature  above  their 
boiling-points,  they  are  generally  heated  in  sealed  tubes.  If  a 
quantitative  determination  is  not  to  be  made,  if  the  substances 
to  be  heated  do  not  attack  the  glass  or  generate  no  gases,  and  if 
the  heating  is  not  to  be  high,  soft  glass  tubes  may  be  used.  But 
generally,  and  in  quantitative  determinations  always,  difficultly 
fusible  tubes  of  potash  glass  are  used,  since  they  are  not  so  easily 
acted  upon  and  do  not  crack  so  readily  as  the  former.  In  filling 
the  tubes  the  following  points  are  observed.  The  tube  is  dried 
before  placing  the  substance  in  it.  Never  put  solid  or  liquid 
substances  directly  in  the  tube,  but  with  the  aid  of  a  funnel- tube 
which  should  be  as  wide  as  possible  when  the  substance  is  a  solid. 
In  proportion  to  the  temperature  of  the  heating  a  greater  or  less 
pressure  is  developed ;  therefore  more  or  less  of  the  substance  is 
placed  in  the  tube,  depending  on  the  conditions.  The  tube  is 
never  more  than  half-filled.  Easily  volatile  substances  as  well 
as  those  giving  off  vapours,  like  hydrochloric  and  hydriodic  acids, 
which  render  the  sealing  of  the  tube  difficult,  are  transferred  to 
the  tube  just  before  the  sealing  is  to  be  done.  In  withdrawing 
the  funnel-tube  care  is  taken  to  avoid  bringing  it  in  contact 
with  the  walls  of  the  tube. 

Sealing.  —  To  seal  the  open  end  of  a  tube  charged  with  the 
substance,  it  is  warmed  by  holding  it  at  an  angle  of  about  45°, 
with  constant  turning,  in  the  small  luminous  flame  of  a  blast- lamp, 
and  then  heated  strongly  in  a  larger  non-luminous  flame ;  when 
the  glass  becomes  soft,  a  previously  somewhat  warmed  glass  rod 
is  fused  to  it  (Fig.  43,  I).  The  flame  is  then  applied  to  the  tube 
at  a  short  distance  from  the  opening,  and  as  soon  as  the  glass  has 
become  soft  the  tube  is  narrowed  by  drawing  it  out  suddenly  (II). 
After  breaking  off  or  cutting  off  the  end  of  the  capillary  tube  at 
z,  to  allow  the  air  to  escape  on  further  heating,  it  is  heated  at  b, 
when  the  tube  is  softened  at  this  point  it  is  drawn  out  slightly, 


64 


GENERAL  PART 


the  heat  is  applied  just  below  £,  it  is  drawn  out  again,  and  so 
on ;  the  result  is  that  the  form  of  the  end  of  the  tube  gradually 
changes  from  a  cylinder  to  a  sharp-pointed  cone.  The  narrowest 
part  of  the  latter  is  then  heated  with  a  not  too  large  flame 
without  drawing  it  further.  The  soft  glass  melts  together,  and 
there  is  thus  obtained  a  thick-walled  capillary  tube  which  •  is 
melted  off  at  the  proper  place  (III).  Figure  44  shows  the 
sealed  portion  of  a  tube  in  its  natural  size.  In  the  formation  of 


-a 


ii 
FIG.  43. 


Ill 


FIG.  44. 


the  capillary  portion,  it  is  desirable  not  to  turn  the  tube  in  the 
manner  previously  directed,  but  to  give  it  a  few  turns  in  one  direc- 
tion and  then  to  reverse  the  motion,  otherwise  a  spiral  would  be 
formed  owing  to  the  smallness  of  the  glass  at  that  point.  After 
sealing,  the  heated  portion  is  cooled  gradually  by  holding  it  in 
the  luminous  flame  until  it  is  blackened.  The  sealing  of  hard 
glass  tubes  may  be  facilitated  by  placing  a  brick  or  tile  near  the 
flame  in  such  a  position  that  the  heat  will  be  reflected.  If  ^na 


HEATING  UNDER   PRESSURE  6$ 

is  in  possession  of  a  cylinder  of  oxygen,  it  may  be  attached  to 
the  blast-lamp  in  place  of  the  blast.  At  the  high  temperature 
of  the  illuminating  gas:oxygen  flame,  the  sealing  may  be  effected 
with  great  ease. 

In  many  cases  the  operation  is  rendered  difficult  by  the  vapours 
of  the  substance  attacking  the  glass,  or  by  the  decomposition  of 
the  substance  with  the  evolution  of  troublesome  products  like 
carbon,  iodine,  etc.  Under  these  conditions,  the  tube  is  not 
drawn  out  first  to  a  narrow  tube,  as  above,  but  the  glass  rod 
fused  on  is  allowed  to  remain,  and  this  is  used  to  draw  out  the 
tube.  The  sealing  is  rendered  less  difficult  by  allowing  the  air 
to  have  free  access  to  the  tube,  in  order  that  the  evolved  vapour 
may  pass  out  unimpeded.  The  separation  of  carbon  may  be 
avoided  by  having  an  assistant  direct  a  continuous  current  of  air, 
during  the  heating,  through  a  narrow  tube  into  the  upper  part 
of  the  tube  being  sealed ;  this  will  cause  the  oxidation  of  the 
carbon.  When  dealing  with  very  volatile  substances,  during  the 
sealing  the  lower  part  of  the  tube  is  cooled  by  water,  ice,  or  a 
freezing  mixture.  In  this  case,  the  services  of  an  assistant  will 
be  needed  to  give  to  the  vessel  containing  the  cooling  agent  a 
circular  motion  corresponding  to  that  of  the  tube.  Under  these 
conditions,  it  is  often  advisable  to  narrow  the  tube  before  charging 
it  with  the  substance,  so  that  it  will  just  admit  a  funnel-tube  as 
narrow  as  possible. 

Heating.  —  The  heating  of  sealed  tubes  (bombs)  is  conducted 
in  the  so-called  "  bomb-furnace,"  of  which  a  convenient  form  is 
represented  in  Fig.  45.  To  be  able  to  carry  out  the  operation  of 
heating  at  a  definite  temperature,  a  cork,  covered  with  asbestos 
paper,  bearing  a  thermometer,  is  fitted  into  the  opening  at  the 
top  of  the  furnace.  The  bulb  of  the  thermometer  must  be  about 
i  cm.  above  the  bottom  of  the  iron  tube.  The  sealed  tube  is  not 
heated  directly,  but  in  a  thick- walled  protecting  case  of  iron 
closed  at  one  end,  in  which  the  glass  tube  is  so  placed  that  the 
capillary  portion  is  at  the  open  end.  In  transferring  the  glass 
tube  to  the  iron  casing  the  latter  is  not  held  vertically,  but  is 
slightly  inclined  from  the  horizontal,  so  that  the  glass  tube  may 


66 


GENERAL   PART 


not  be  broken  by  suddenly  striking  the  bottom.  The  iron  casft 
is  pushed  into  the  furnace  open  end  first,  so  that  in  case  of  an 
explosion  the  fragments  of  glass  are  not  thrown  out  of  the  for- 
ward end  but  from  the  rear  of  the  furnace,  directed  toward  a  wall. 
A  "fragment  cage"  renders  the  flying  pieces  of  glass  harmless. 
After  the  tube  is  in  position  the  front  opening  is  closed  by  a 
"  drop-slide."  The  tubes  are  not  heated  at  once  up  to  the  desired 
temperature,  but  are  warmed  gradually.  If  it  is  desired  to 
heat  a  furnace  similar  to  the  one  represented  to  a  low  tempera- 
ture, the  gas  tubes  are  raised  and  small  flames  used,  rather  than 
a  lowering  of  the  gas-tube  and  the  corresponding  increase  in  size 


FIG.  45. 

of  flame.  The  danger  of  the  bursting  of  the  glass  tubes  may 
be  diminished  in  many  cases,  particularly  in  those  in  which  a 
very  high  pressure  is  developed,  by  interrupting  the  heating  after 
a  certain  length  of  time,  opening  the  capillary  after  the  tube  has 
completely  cooled,  and  allowing  the  gases  which  have  been  gen- 
erated to  escape.  The  tube  is  then  resealed  and  heated  again. 

If  tubes  are  to  be  heated  not  higher  than  100°,  the  convenient 
so-called  "  water-bath  cannon  "  is  used,  in  which  the  case  enclos- 
ing the  tube  is  heated  by  steam  at  ordinary  pressure ;  in  this  case 
overheating  is  impossible. 

Opening  the  Tubes.  —  Sealed  tubes  must  not  be  opened  until 
after  they  are  completely  cold.  The  protecting  case  of  iron,  con- 
taining the  tube,  is  removed  from  the  furnace  and  held  in  a  slightly 


HEATING   UNDER   PRESSURE  6/ 

inclined  position,  the  end  of  the  capillary  being  higher  than  the 
rear  end.  By  means  of  a  slight  jerk  the  capillary  end  of  the  glass 
tube  is  caused  to  project  from  the  iron  case.  The  extreme  end 
of  the  capillary  is  now  held  in  the  flame  of  a  Bunsen  burner.  In 
case  there  is  an  internal  pressure  in  the  tube,  the  glass  on  becom- 
ing soft  will  be  blown  out  and  the  gases  will  escape  from  the 
opening  thus  made,  often  with  such  force  as  to  extinguish  the 
flame.  If  on  the  softening  of  the  glass  the  capillary  is  not  blown 
out,  it  may  be  due  to  the  absence  of  internal  pressure  or  the  tube 
may  be  stopped  up  by  some  of  the  substance.  In  the  latter  case 
the  substance  is  removed  by  heating.  To  show  that  there  is  an 
internal  pressure  the  capillary  is  held  after  it  has  been  opened 
near  a  small  luminous  flame ;  if  the  latter  is  blown  out  in  a  long 
thin  flame  sidewise,  obviously  there  is  pressure.  If  great  pressure 
exists  in  a  tube  to  be  opened,  before  blowing  the  capillary  the 
hand  holding  the  iron  casing  is  protected  by  a  thick  glove  or  a 
cloth  is  wrapped  around  the  casing  several  times  at  the  point 
where  it  is  held,  so  that  if  the  tube  bursts,  in  consequence  of  the 
sudden  diminution  of  pressure,  and  the  seam  of  the  case  should 
be  torn  open,  the  hand  is  protected  from  injury.  In  handling  an 
unopened  tube  the  greatest  care  possible  must  be  observed.  It  is 
never  removed  from  the  iron  casing  to  look  at  it  or  for  any  other 
purpose.  On  opening,  it  is  held  in  such  a  position  that  neither 
the  operator  nor  any  one  else  can  be  injured  in  case  of  bursting. 

On  heating  substances  with  hydriodic  acid  and  phosphorus,  it 
sometimes  happens,  that  the  tube  on  being  opened  by  a  flame, 
explodes.  In  this  case  the  explosion  is  -due  to  the  fact  that  the 
phosphine  as -well  as  the  hydrogen  evolved  in  the  reaction  have 
formed  an  explosive  mixture  with  the  oxygen  of  the  air  present 
in  the  tube.  Under  these  conditions,  the  capillary  is  opened  by 
snipping  off  the  end  with  pincers  or  tongs,  but  in  doing  so  the 
greatest  care  must  be  observed.  To  remove  the  end  of  the  cone, 
it  is  not  necessary  to  proceed  as  described  below,  but  the  end 
of  the  tube  is  broken  directly  with  a  blow  of  a  hammer. 

In  order  to  break  off  the  end  of  a  tube  after  it  has  been  opened, 
so  that  the  contents  may  be  emptied  out,  the  procedure  is  as 


68  .  GENERAL  PART 

follows  :  At  that  point  of  the  tube  where  the  cone  begins,  a  well- 
defined  file  mark  is  made,  not  extending  completely  around  the 
tube ;  this  is  touched  lightly  with  the  hot  end  of  a  glass  rod, 
previously  heated  to  fusion  in  the  blast-flame.  If  the  crack  caused 
by  this  does  not  extend  entirely  around  the  tube,  the  extreme 
end  of  it  is  again  touched  with  a  hot  glass  rod,  by  which  it  is 
extended,  so  that  the  conical  end  may  be  lifted  off.  Instead  of  a 
glass  rod,  a  thick  iron  wire,  the  end  of  which  has  been  bent  around 
the  iron  casing  to  a  semicircle,  may  be  used.  If  this  is  heated 
to  redness,  the  file  mark  touched  with  it,  and  the  wire  turned,  the 
end  of  the  tube  breaks  off  smoothly.  To  prevent  the  fragments 
of  glass  from  falling  into  the  tube  (when  a  quantitative  determina- 
tion is  being  made),  the  method  of  procedure  is  this  :  As  before, 
a  deep  file  mark  is  made,  and  on  each  side  of  it,  at  a  distance 
of  ^  cm.,  a  strip  of  moistened  filter-paper  i  cm.  wide  is  wrapped 
around  the  tube  several  times.  That  portion  of  the  tube  between 
the  strips  is  heated  by  a  small  flame,  the  tube  being  con- 
stantly turned,  this  causes  the  end  to  split  off  smoothly 
without  splintering.  If  the  glass  does  not  crack  at  once, 
the  heated  portion  is  moistened  with  a  few  drops  of 
water,  and  the  breaking  off  will  follow  with  certainty. 

Volhard  Tubes.  —  The  tube  described  by  Volhard 
(Fig.  46)  may  be  used  to  great  advantage  when  it  is 
desired  to  heat  large  quantities  of  substances  in  a  single 
tube.  It  consists  of  a  wide  tube  to  the  end  of  which  a 
narrower  one  is  fused.  A  tube  of  this  kind,  35  mm.  in 
diameter  and  45  cm.  in  length,  contains  about  \  of  a 
litre,  and  possesses  the  further  advantage  of  being  easy 
to  seal.  If  on  opening  the  tube  care  be  taken  to  cut 
off  as  small  a  portion  of  the  narrow  end  as  possible, 
it  may  be  used  repeatedly.  If,  finally,  the  narrowed 
portion  becomes  too  short,  another  piece  of  the  same 
kind  of  tubing  is  sealed  on. 

Pressure  Flasks.  Autoclaves.  —  In  order  to  heat  substances 
under  pressure  at  a  moderate  temperature  which  on  reacting  with 
each  other  evolve  no  gaseous  products,  so  that  no  pressure  due 


Jl 


HEATING   UNDER   PRESSURE 


to   the   reaction  is  developed,   they  are   sometimes   enclosed    in 

strong-walled  flasks  (pressure  flasks),  wrapped  up  in  a  cloth  and 
heated  in  a  water-bath. 

Very  well  adapted  to  this  purpose  are  the  common 
soda-water  or  beer  bottles,  of  the  kind  represented 
in  Fig.  47.  In  using  them  they  are  not  immersed  in 
water  already  heated,  but  are  slowly  heated  with  the 
water.  The  water-bath  is  closed  by  a  loosely  fitting 
cover,  so  that  in  case  the  bottle  bursts,  one  may  not 
be  burned  by  the  hot  water.  The  flasks  are  not 
opened  until  after  they  are 
completely  cold. 

Large    quantities   of   sub- 
stances which  do  not  act  on  metals  may 

be  heated  under  pressure  in  closed  ves- 
sels, generally  made  of  iron,  bronze  or 

copper   (autoclaves).     Such  vessels  are 

not  suited   for  heating  acid   substances, 

but  may  be  used  for  neutral  or  alkaline 

substances.     In  this  laboratory  Mannes- 

mann  tubes  (without  seams)  are  in  use, 

one  end  being  welded  together,  and  the 

other   is   supplied  with    a   screw-thread 

and  cap.     The  open  end  is  cone-shaped. 

The  tube  is  closed  by  a  threaded  cap, 

which  in  section  shows  a  cone.    The  cap 

is   partially  filled  with  lead.     After  the 

substance  has  been  put  in,  the  cover  is 

screwed  on  as  far  as  possible  with  the 

hand,   the   tube   is   then   clamped    in    a 

vise,    and    the    cap    made    fast   with    a 

wrench.     The  conical  end  of  the  tube  is 

pressed   into  the   soft  lead,  thus  giving 

an  excellent  joint.     The  heating  may  be 

conducted  in  an  oil-bath,  or  directly  in  the  bomb-furnace.     If  the 

heating  is  to  be  carried  beyond  the  point  at  which  lead  softens,  a 


FIG.  48. 


70  GENERAL   PART 

short  metallic  condenser  about  10  cm.  in  length  may  be  screwed 
on  the  threaded  portion  of  the  tube.  A  slow  current  of  water  is 
passed  through  the  condenser. 

Another  form  of  autoclave  is  represented  in  Fig.  48.  For  the 
packing  a  ring  of  lead  or  asbestos  is  used.  The  tube  leading  to 
the  interior  is  designed  for  a  thermometer.  The  lower  portion 
contains  oil  in  which  the  thermometer  is  placed. 


MELTING-POINT 


MELTING-POINT 

In  organic  work  the  most  common  method  of  testing  the 
purity,  of  characterising  and  of  recognising  a  solid  compound, 
is  the  determination  of  its  melting-point.  The  apparatus  most 
generally  used  for  this  purpose  is  represented  in  Figs.  49  and  50. 
A  long-necked  flask  is  closed  by  a  cork  provided  ;vith  several 
canals  cut  in  the  sides,  through  which  the  heated  air  and  vapours 

may  escape,  bearing  a  thermometer. 
The  bulb  of  the  flask  is  two-thirds 
rilled  with  pure  concentrated  sul- 
phuric acid,  into  which  is  dropped 
a  crystal  of  .potassium  nitrate  the 
size  of  a  pin-head,  to  prevent  it 
from  becoming  dark  in  colour.  The 
substance  is  placed  in  a  small  nar- 
row tube  (melting-point  tube),  made 
in  the  following  way :  A  glass  tube 
4-5  mm.  wide  is  heated  at  one  point 
while  constantly  turned,  in  a  small, 
blast-lamp  flame,  until  it  becomes 
soft,  and  is  then  drawn  out  from 
— Ct  both  ends  to  a  tube  i  mm.  wide. 
The  narrow  tube  thus  produced  is 
then  fused  off  at  its  middle  point ; 
the  portion  lying  next  to  that  part 
of  the  glass'  tube  which  has  not  been  drawn  out  is  heated  as 
before  and  is  again  drawn  out,  and  so  on.  There  is  thus  pro- 
duced a  tube  having  the  form  represented  in  Fig.  51  a.  In 
order  to  prepare  the  melting-point  tube  from  this  a  file-mark  is 
made  at  the  points  indicated,  the  tube  broken  off  and  fused  at 
the  narrow  end  by  holding  it  nearly  vertical  in  a  Bunsen  flame. 
Fig.  51  b  represents  the  melting-point  tube  in  its  natural  size. 
A  supply  of  several  dozen  of  these  is  made  and  preserved  in  a 
closed  bottle.  To  transfer  to  the  tube  the  substance  the  melt- 


FIG.  49. 


FIG.  50. 


72  GENERAL   PART 

ing-point  of  which  is  to  be  determined,  a  small  portion  of  it  is 
pulverised,  the  end  of  the  tube  dipped  into  it ;  by  gentle  tapping 
the  substance  is  caused  to  fall  from  the  upper  end  to  the  bot- 
tom of  the  tube.  In  order  that  it  may  not  form  a 
too  loose  layer,  it  is  packed  by  a  thin  glass  rod  or 
platinum  wire.  The  height  of  the  layer  should  be 
i  mm.  and  in  no  case  more  than  2  mm.  To  attach 
the  tube  different  methods  may  be  used.  The 
upper  end  of  the  tube  may  be  touched  with  a  drop 
of  sulphuric  acid ;  this,  when  brought  in  contact 
with  the  thermometer,  will  cause  it  to  adhere.  It 
is  safer  to  fasten  the  tube,  just  below  the  mouth,  to 
the  thermometer  with  a  thin  platinum  wire  or  a 
rubber  ring  i  mm.  wide.  The  substance  is  placed 
at  the  middle  point  of  the  thermometer  bulb. 
The  thermometer  is  now  immersed  in  the  sul- 
phuric acid  until  the  bulb  is  at  about  the  centre  of 
the  liquid ;  the  flask  is  heated  with  a  free  flame 
which  is  given  a  continuous,  uniform  motion  as  in 
distillation.  The  burner  is  inclined  at  a  conven- 
ient angle,  so  that,  if  the  flask  should  break,  the 
hand  would  not  be  directly  under  it.  When  the 
melting  temperature  is  reached,  it  is  observed  that 
the  previously  opaque,  unfused  substance  suddenly 
becomes  transparent  and  a  meniscus  is  formed  on 
its  upper  surface.  If  it  is  known  at  about  what 
point  the  substance  will  melt,  it  may  be  heated 
rapidly  to  within  10°  of  this  point,  and  then  slowly 
with  a  small  flame  so  that  the  behaviour  of  the  sub- 
stance from  degree  to  degree  can  be  easily  observed. 
If  the  melting-point  is  not  known,  it  can  be  readily  a  * 

ascertained  on  heating  it  rapidly  to  a  high  tempera- 
ture.    In  this  case  the  determination  is  repeated,  heating  rapidly 
until  the    temperature    approaches   the    melting-point,  and  then 
slowly.     In  many  cases  when  the  temperature  nears  the  melting- 
point  this  is  shown  by  a  softening  of  the  substance  before  melt- 


MELTING-POINT 


73 


ing ;  it  loosens  from  the  walls  of  the  tube  and  collects  in  the 
middle.  If  this  phenomenon  occurs  the  heating  is  conducted 
very  slowly  from  degree  to  degree.  At  times  proximity  to  the 
melting-point  may  also  be  recognised  by  the  fact  that  the  par- 
ticles of  the  substance  which  adhered  to  the  upper  portion  of 
the  tube  during  the  filling,  melt  before  the  mass  of  the  sub- 
stance ;  since  the  hotter  and  therefore  lighter  layers  of  the  acid 
rise  to  the  top,  the  upper  layers  of  the 
bath  are  heated  somewhat  higher  than 
the  lower. 

Instead  of  the  apparatus  just  de- 
scribed the  one  represented  in  Fig.  52 
serves  very  well  for  the  same  purpose. 
The  liquid  used  may  be  water  or  sul- 
phuric acid,  depending  on  the  melting- 
point  of  the  substance  to  be  examined, 
or  in  case  of  a  substance  with  a  high 
melting-point  paraffin  is  placed  in  a 
beaker  supported  on  a  wire  gauze.  In 
order  to  keep  the  liquid  at  a  uniform 
temperature,  it  is  stirred  by  an  up-and- 
down  motion  of  the  glass  stirrer  a. 

A  substance  is  regarded  as  pure  in 
most  cases,  if  it  melts  sharply  within 
one-half  or  a  whole  degree,  and  if  after 
repeated  crystallisation  the  melting-point 
does  not  change.  In  determining  the 
melting-point  of  a  newly  discovered  sub- 
stance, one  determination  is  not  sufficient  even  if  it  is  very  sharp ; 
a  small  portion  is  recrystallised  and  the  melting-point  again  deter- 
mined. Many  substances  decompose  on  fusing,  if  this  takes  place 
suddenly  at  a  definite  temperature,  this  may  also  be  regarded  as 
a  characteristic  of  the  substance. 

Since  many  compounds  on  heating  decompose  explosively,  and 
since  in  the  last  few  years  it  has  happened  that  the  explosion  of 
minute  quantities  of  a  compound  has  shattered  the  melting-point 


FIG.  52. 


74 


GENERAL   PART 


apparatus,  and  serious  wounds  have  been  caused  by  the  hot 
sulphuric  acid,  it  is  safer  before  the  melting-point  of  a  hitherto 
unknown  substance  is  determined  in  the  apparatus  described 
above,  to  take  the  slight  trouble  of  making  a  preliminary  test  by 
heating  a  small  tube  containing  the  substance  directly  in  a  small 
flame  to  the  melting  temperature,  and  by  this  means  ascertaining 
if  the  substance  will  explode. 

Testing  the  Thermometer.  —  At  this  point  a  few  observations 
concerning  the  testing  and  correcting  of  the  thermometer  will  be 
added.  Since  the  ordinary  thermometers,  at  least  the  cheaper 
varieties,  are  never  exact,  they  must  be  corrected  before  using. 
If  a  normal  thermometer  is  at  hand,  the  correction  to  be  applied 
may  be  determined  by  slowly  heating  the  thermometer  to  be  tested 
by  the  side  of  the  normal  instrument  in  a  bath  of  sulphuric  acid, 
glycerol,  or  vaseline,  and  noticing  the  reading  of  both  thermometers 
for  every  10°.  There  is  thus  obtained  a  table  from  which  the  cor- 
rections may  be  read  directly.  For  many  purposes  it  is  sufficient 
to  determine  the  deviation  at  only  a  few  points ;  the  corrections 
for  the  degrees  lying  between  these  may  be  calculated  by  inter- 
polation. Thus,  e.g.,  the  point  to  be  considered  as  the  true  zero 
point  may  be  determined  as  follows :  A  thick-walled  test-tube  of 
about  2\  cm.  in  diameter  and  1 2  cm.  in  length  is  one-third  filled 
with  distilled  water.  The  mouth  is  closed  by  a  cork  bearing  a 
thermometer  dipping  into  the  water.  Through  an  opening  cut 
out  of  the  side  of  the  cork  is  introduced  a  thick  copper  wire,  the 
end  of  which  is  bent  into  a  circle  at  a  right  angle  to  its  length. 
The  test-tube  is  surrounded  by  a  freezing  mixture  of  ice  and  salt. 
The  water  is  frequently  agitated  with  the  stirrer ;  the  temperature 
at  which  crystals  first  begin  to  form  is  carefully  noted. 

The  true  100°  point  is  found  by  placing  distilled  water  in  a  not 
too  small  fractionating  flask  and  determining  the  boiling-point  of  it, 
the  entire  column  of  mercury  being  in  the  vapour.  In  an  analo- 
gous manner,  the  boiling-point  of  naphthalene  (218°  at  760  mm. 
pressure)  and  of  benzophenone  (306°  at  760  mm.  pressure)  may 
serve  for  the  correction  of  the  higher  degrees.  Since  the  boiling- 
point  is  influenced  by  the  pressure,  the  barometer  must  be  read  at 


DRYING   AND   CLEANING   OF  VESSELS 


75 


the  same  time  with  the  thermometer  and  a  correction,  taken  from 
the  table  given  below,  applied. 


Pressure. 

Water. 

Naphthalene. 

Benzophenone. 

720  mm. 

98.5° 

2I5.70 

303.50 

725 

98.7 

216.0 

303.8 

730 

98.9 

216.3 

304.2 

735 

99.I 

216.6 

304.5 

740 

99-3 

216.9 

304.8 

745 

99-4 

217.2 

305.2 

750 

99.6 

217.5 

305-5 

755 

99.8 

217.8 

305.8 

760 

IOO.O 

218.1 

306.1 

765 

100.2 

218.4 

306.4 

770 

100-4 

218.7 

306.7 

DRYING  AND   CLEANING   OF  VESSELS 

While  in  analytical  operations,  since  one  generally  deals  with 
aqueous  solutions,  the  cleaned  vessels  may  be  used  even  if  wet,  it 
frequently  happens  in  organic  work,  in  experimenting  with  liquids 
not  miscible  with  water,  that  dry  vessels  must  be  employed.  In 
order  to  dry  small  pieces  of  apparatus  rapidly,  they  should  be 
rinsed  first  with  alcohol  and  then  with  ether.  To  remove  the  last 
portions  of  the  easily  volatile  ether,  air  from  a  blast  is  blown 
through  the'  vessel  for  a  short  time,  or  the  ether  vapours  are 
removed  by  suction.  The  alcohol  and  ether  used  for  rinsing  can 
frequently  be  used  again ;  it  is  convenient  to  keep  two  separate 
bottles  for  the  wash  alcohol  and  wash  ether,  into  which  the  sub- 
stances, after  being  used,  may  be  poured. 

For  rapid  drying  of  large  vessels  this  method  is  costly.  In  this 
case  the  procedure  is  as  follows :  The  wet  vessel  is  first  drained 
as  thoroughly  as  possible,  and  then  heated  with  constant  turning 
in  a  large  luminous  blast-flame,  while,  by  means  of  a  blast  of  air 
from  bellows  or  other  source,  the  water  vapour  is  driven  out.  It 
may  also  be  removed  by  careful  heating  and  simultaneous  suction. 


76  GENERAL   PART 

Thick-walled  vessels  like  suction  flasks  must  not  be  heated  over 
a  flame,  but  are  dried  by  the  first  method. 

Vessels  may  be  cleaned  in  part  by  rinsing  them  out  with  water 
with  the  use  of  a  feather  or  flask-cleaner.  If  the  last  portions 
of  the  solution  of  a  solid,  e.g.  in  alcohol,  are  to  be  removed  from 
a  flask,  it  is  not  washed  out  at  once  with  water,  but  first  with  a 
small  quantity  of  the  solvent,  and  then  afterwards  with  water. 
If  the  vessel  contained  a  liquid  not  miscible  with  water,  it  is  first 
washed  with  alcohol  and  then  with  water.  Resinous  or  tarry 
impurities  adhering  firmly  to  the  walls  can  be  removed  by  crude 
concentrated  sulphuric  acid.  The  action  of  this  latter  may  be 
strengthened  by  adding  a  little  water  to  it,  by  which  heat  is  gener- 
ated ;  also  by  the  addition  of  some  crystals  of  potassium  dichro- 
mate.  At  times  the  impurities  adhere  so  firmly  that  the  vessel 
must  be  allowed  to  stand  in  contact  with  sulphuric  acid  for  a  long 
time.  Crude  concentrated  nitric  acid,  or  a  mixture  of  this  with 
sulphuric  acid,  is  also  used  at  times  for  cleaning  purposes.  Im- 
purities of  an  acid  character  can,  under  certain  conditions,  be 
removed  by  caustic  soda  or  caustic  potash. 

Finally,  a  method  for  cleaning  the  hands  may  be  mentioned  if 
they  are  discoloured  by  dyes  which  cannot  be  removed  by  water. 
If  the  dye,  e.g.  fuchsine,  contains  an  amido  (NH2)  group,  the  hands 
are  dipped  into  a  dilute,  weakly  acid  solution  of  sodium  nitrite. 
The  dye  is  diazotised,  and  may  be  removed  by  washing  in  water. 
The  two  methods  following  are  applicable  to  all  dyes ;  the  hands 
are  immersed  into  a  dilute  solution  of  potassium  permanganate 
to  which  some  sulphuric  acid  has  been  added,  and  are  allowed  to 
remain  for  some  time  ;  the  dye  is  oxidised,  and  thereby  destroyed. 
After  the  permanganate  has  been  washed  off  with  water,  the  hands, 
especially  the  nails,  are  coloured  brown  by  manganese  dioxide. 
This  is  removed  by  washing  the  hands  with  a  little  sulphurous  acid, 
or  oxalic  acid  (ammonium  oxalate  plus  hydrochloric  or  sulphuric 
acid).  The  second  method  is  this  :  A  thick  paste  of  bleaching 
powder  and  a  sodium  carbonate  solution  is  rubbed  on  the  hands. 
This  causes  the  oxidation  and  destruction  of  the  dye  as  above.  In 
order  to  take  away  the  unpleasant  odour  of  the  bleaching  powder, 
the  hands  are  scrubbed  with  a  brush,  care  being  taken  to  remove 
the  particles  adhering  to  the  upper  and  under  surface  of  the  nails, 
and  are  then  washed,  as  just  described,  with  sulphurous  acid,  or 
oxalic  acid. 


ORGANIC   ANALYTICAL   METHODS  7; 


ORGANIC    ANALYTICAL    METHODS 

DETECTION  OF  CARBON,  HYDROGEN,  NITROGEN,  SULPHUR,  AND  THE 

HALOGENS 

Tests  for  Carbon  and  Hydrogen.  —  If  on  heating  a  substance  on 
platinum  foil,  it  burns  with  a  flame  (exceptions,  e.g.  S),  or  de- 
composes with  charring,  it  is  an  organic  substance.  Carbon  and 
hydrogen  may  be  detected  in  one  operation,  by  mixing  a  small 
portion  of  the  dried  substance  with  several  times  its  volume  of 
ignited  fine  cupric  oxide,  placing  the  mixture  in  a  small  test-tube, 
adding  more  cupric  oxide  to  the  top  of  the  mixture,  and  heating 
strongly,  the  tube  being  closed  by  a  cork  bearing  a  delivery  tube 
bent  twice  at  right  angles.  If  the  gas  evolved  (carbon  dioxide) 
will  cause  a  clear  solution  of  barium  hydroxide  to  become  turbid, 
the  original  substance  contained  carbon  ;  if  it  also  contained  hy- 
drogen, small  drops  of  water  will  collect  in  the  upper  cold  part  of 
the  tube. 

Test  for  Nitrogen.  —  To  test  an  organic  substance  for  nitrogen, 
it  is  heated  in  a  small  test-tube  of  difficultly  fusible  glass,  about 
5  mm.  wide  and  6  cm.  long,  with  a  piece  of  bright  potassium  the 
size  of  a  lentil,  which  has  been  pressed  between  layers  of  filter- 
paper,  in  a  Bunsen  flame  until  decomposition,  generally  accom- 
panied by  slight  detonations  and  dark  colouration,  takes  place. 
The  tube  is  finally  heated  to  redness ;  while  still  hot  it  is  dipped 
into  a  small  beaker  containing  10  c.c.  of  water;  by  this  the  tube 
is  shattered,  and  any  potassium  unacted  upon  becomes  ignited. 
The  aqueous  solution  containing  potassium  cyanide,  if  nitrogen 
was  present  in  the  substance,  is  filtered  from  the  carbon  and  glass 
fragments,  the  filtrate  treated  with- a  few  drops  of  caustic  potash 
or  caustic  soda  until  it  shows  an  alkaline  reaction ;  to  this  solution 
is  then  added  a  small  quantity  of  ferrous  sulphate  solution  and 
ferric  chloride  solution  ;  it  is  boiled  1-2  minutes,  and  if  potassium 
cyanide  was  present,  potassium  ferrocyanide  will  be  formed.  After 
cooling,  the  alkaline  liquid  is  acidified  with  hydrochloric  acid,  the 


78  GENERAL   PART 

precipitated  ferric  and  ferrous  hydroxides  will  be  dissolved,  and 
being  acted  upon  by  the  potassium  ferrocyanide,  will  form  Berlin 
blue.  Accordingly,  if  nitrogen  was  present,  a  blue  precipitate  is 
obtained,  otherwise  only  a  yellow  solution  will  be  formed.  If  the 
substance  contains  only  a  small  proportion  of  nitrogen,  at  times  no 
precipitate  is  obtained  at  first,  but  only  a  bluish-green  solution. 
If  this  is  allowed  to  stand  some  time,  under  certain  conditions, 
ever  night,  the  precipitate  will  separate  out.  In  testing  easily 
volatile  substances  for  nitrogen,  a  longer  tube  is  used  and  the  por- 
tions of  substance  condensing  in  the  upper  cold  part  of  the  tube 
flow  back  a  number  of  times  on  the  potassium.  In  place  of  potas- 
sium, sodium  may  also  be  used  in  most  cases,  but  the  former  acts 
more  certainly.  In  testing  for  nitrogen,  in  a  substance  containing 
sulphur,  a  larger  quantity  of  potassium  or  sodium  than  that  given 
above  is  used  (for  0.02  grm.  of  substance,  about  0.2  grm.  potassium, 
in  order  to  prevent  the  formation  of  an  alkali  sulphocyanate). 
Substances  which  evolve  nitrogen  at  moderate  temperatures,  e.g. 
diazo-compounds,  cannot  be  tested  in  the  manner  described.  In 
dealing  with  a  substance  of  this  kind  it  must  be  determined  whether 
on  heating  the  substance  with  cupric  oxide  in  a  tube  filled  with  car- 
bon dioxide,  a  gas  is  given  off  which  is  not  absorbed  by  a  solution 
of  caustic  potash.  (See  quantitative  determination  of  nitrogen.) 

In  a  limited  number  of  substances  containing  nitrogen,  the  pres- 
ence of  the  latter  may  be  proved  by  heating  the  substance  with  an 
excess  of  pulverised  soda-lime  in  a  test-tube  with  a  Bunsen  flame ; 
this  causes  decomposition  with  evolution  of  ammonia,  which  is 
detected  by  its  odour  or  by  means  of  a  black  colour  imparted  to  a 
piece  of  filter-paper  moistened  with  a  solution  of  mercurous  nitrate. 
Nitro-compounds,  e.g.,  do  not  give  this  reaction. 

Test  for  Sulphur.  —  The  qualitative  test  for  sulphur  is  made  in 
the  same  manner  as  that  for  nitrogen.  The  substance  is  heated 
in  a  small  tube  with  sodium.  After  the  mass  has  cooled  it  is 
treated  with  water,  and  to  one-half  of  the  solution  is  added  a 
small  quantity  (a  few  drops)  of  a  solution  of  sodium  nitroprus- 
siate,  just  prepared  by  shaking  a  few  crystals  with  water  at  the 
ordinary  temperature.  A  violet  colouration  indicates  the  presence 


ORGANIC  ANALYTICAL   METHODS  79 

of  sulphur.  Since  the  nitroprussiate  reaction  is  very  delicate,  no 
conclusion  as  to  the  amount  of  sulphur  can  be  drawn  from  the 
test,  therefore  the  second  half  of  the  solution  is  treated  with  a 
lead  acetate  solution  and  acidified  with  acetic  acid.  In  propor- 
tion to  the  amount  of  lead  sulphide  formed,  the  liquid  will  assume 
a  dark  colour,  or  a  more  or  less  heavy  precipitate  will  appear,  in 
this  way  indicating  the  original  quantity  of  sulphur. 

Easily  volatile  substances  cannot  usually  be  tested  by  this 
method.  They  are  heated  with  fuming  nitric  acid  in  a  bomb- 
tube  to  about  200  or  300°.  After  diluting  with  water  the  solution 
is  tested  with  barium  chloride  for  sulphuric  acid.  (See  method  for 
the  quantitative  determination  of  sulphur.) 

Test  for  the  Halogens.  —  The  presence  of  chlorine,  bromine, 
.and  iodine  in  organic  compounds  can  only  in  rare  cases  be  shown 
by  precipitation  with  silver  nitrate.  This  is  explained  by  the  fact 
that  most  organic  compounds  are  non-electrolytes ;  i.e.  that  the 
solutions  of  the  same  do  not  contain  free  halogen  ions,  as  is  the 
case  in  solutions  of  the  inorganic  salts  of  the  halogen  hydracids. 

In  order  to  detect  the  halogens,  the  substance  to  be  tested  is 
heated  in  a  not  too  narrow  test-tube  with  a  Bunsen  flame  with  an 
excess  of  chemically  pure  lime,  the  tube  while  still  hot  is  dipped 
into  a  little  water,  chemically  pure  nitric  acid  is  added  to  acid 
reaction,  the  solution  is  then  filtered  and  treated  with  silver  nitrate. 

In  compounds  containing  no  nitrogen,  a  test  for  the  halogens 
may  be  made  by  the  same  method  given  for  nitrogen  —  heating 
with  sodium.  In  this  case  the  solution,  filtered  from  the  decom- 
position products  and  fragments  of  glass,  is  acidified  with  nitric 
acid  and  silver  nitrate  added.  .Substances  containing  nitrogen 
cannot  be  tested  in  this  way  for  the  halogens,  since,  as  shown 
above,  these  on  fusion  with  sodium  give  sodium  cyanide,  which, 
like  the  sodium  halides,  reacts  with  silver  nitrate. 

The  presence  of  halogens  may  be  recognised  very  quickly  and 
conveniently  by  Beilstein's  test.  A  piece  of  cupric  oxide  the  size 
of  a  lentil,  or  a  small  rod  of  the  oxide  \  cm.  long,  is  wrapped 
around  with  a  thin  platinum  wire,  the  other  end  of  which  is  fused 
to  a  glass  handle,  and  heated  in  the  Bunsen  flame  until  it  becomes 


8O  GENERAL   PART 

colourless.  If,  after  cooling,  a  minute  particle  of  the  substance  con- 
taining a  halogen  is  placed  on  this  and  then  heated  in  the  outer  part 
of  the  flame,  the  carbon  burns  first  and  a  luminous  flame  is  noticed. 
This  soon  vanishes,  and  there  appears  a  green  or  bluish-green  colour 
due  to  the  vaporisation  of  the  copper  halide.  From  the  length  of 
time  the  colour  is  visible,  conclusions  may  be  drawn  concerning  the 
presence  of  a  trace  or  more  of  the  halogen  in  the  original  substance. 


QUANTITATIVE  DETERMINATION    OF   THE  HALOGENS 
CARIUS'   METHOD 

The  method  consists  in  heating  a  weighed  amount  of  the  sub- 
stance to  be  analysed  in  a  sealed  glass  tube  with  silver  nitrate  and 
fuming  nitric  acid,  by  which  it  is  completely  decomposed  (oxidised), 
and  weighing  the  quantity  of  the  silver  halide  thus  formed. 

Requisites  for  the  analysis  : 

1.  A  tube  of  difficultly  fusible  glass  sealed  at  one  end,  length 

about  50  cm.;  outside  diameter,  18-20  mm.;  thickness  of 
walls,  about  2  mm.  (Sealing- tubes,  bomb-tubes.) 

2.  A  funnel-tube  about  40  cm.  long,  for  transferring  the  silver 

nitrate  and  nitric  acid  to  the  glass  tube. 

3.  A  weighing-tube  of  hard  glass  (length,  7  cm. ;  outside  diameter, 

.about  6-8  mm.). 

4.  Solid  silver  nitrate  and  pure  fuming  nitric  acid.    The  purity  of 

the  latter  is  tested  by  diluting  2  c.c.  of  it  with  50  c.c.  of  distilled 
water,  and  adding  a  few  drops  of  a  silver  nitrate  solution. 
Neither  an  opalescence  nor  a  precipitate  should  appear. 

Filling  and  Sealing  the  Tube.  —  After  the  bomb-tube,  weighing- 
tube,  and  funnel-tube  have  been  cleaned  with  distilled  water,  they 
are  dried,  not  with  alcohol  and  ether,  but  by  heating  over  a  flame. 
(See  page  75,  Drying.)  The  exact  weight  of  the  weighing-tube 
is  next  determined.  Into  this,  with  the  help  of  a  spatula,  is  placed 
0.15  to  0.2  gramme  of  the  substance  to  be  analysed,  finely  powdered. 
The  open  end  of  the  tube  is  wiped  off  with  a  cloth,  and  the  exact 


ORGANIC  ANALYTICAL  METHODS  8 1 

weight  of  the  tube  plus  the  substance  is  found.  With  the  aid  of 
the  funnel-tube,  about  0.5  gramme  of  finely  powdered  silver  nitrate 
is  transferred  to  the  bomb-tube  (a  correspondingly  larger  amount 
up  to  i  gramme  is  used  for  substances  containing  a  high  percent- 
age of  halogen)  and  2  c.c.  of  fuming  nitric  acid.  If  a  number  of 
halogen  determinations  are  to  be  made,  it  is  advisable  to  measure 
off  2  c.c.  of  water  in  a  narrow  test-tube,  mark  the  volume  with  a 
file  on  the  outside,  and  then  use  this  to  measure  the  acid  for  the 
different  determinations.  After  removing  the  funnel-tube,  care 
being  taken  not  to  touch  the  walls  of  the  bomb-tube  with  it,  the 
weighing-tube  is  inserted  in  the  bomb  held  at  a  slight  angle,  and 
is  allowed  to  slide  down  to  the  bottom,  but  the  substance  must 
not  come  in  contact  with  the  acid.  The  tube  is  now  sealed  in 
the  manner  described  on  page  63.  During  the  sealing,  the  sub- 
stance must  be  prevented  from  coming  in  contact  with  the  acid. 
Even  after  the  tube  is  closed,  this  is  not  brought  about  purposely, 
as  by  violently  shaking  the  tube. 

If  the  substance  to  be  analysed  is  liquid,  it  is  placed  in  the 
weighing-tube  with  a  capillary  pipette,  otherwise  the  procedure  is 
just  as  described.     In    dealing   with   easily   volatile    sub-     ^^ 
stances,  the  weighing- tube  is  closed  by  a  glass    stopper,      jjJF 
made  by  heating  a  piece  of  glass  rod  in  the  blast-flame 
until  it  softens,  and  then  pressing  it  on  a  metal  surface 
until  a  head  is  formed  (Fig.  53). 

Heating  the  Tube.  —  After  cooling,  the  tube  is  trans- 
ferred to  the  iron  protecting  case,  and  heated  in  the  bomb- 
furnace,  in  accordance  with  the  directions  on  page  65. 
The  temperature  and  time  of  heating  depend  upon  the  greater  or 
less  ease  with  which  the  compound  is  decomposed.  In  many 
cases,  it  is  necessary  to  heat  aliphatic  compounds,  or  aromatic 
compounds  that  oxidise  easily,  2-4  hours  at  a  temperature  of 
150-200°,  while  substances  that  do  not  easily  oxidise,  especially 
those  that  contain  sulphur,  must  be  heated  8-10  hours,  and 
finally  up  to  250-300°.  In  this  case  it  is  convenient  to  so 
plan  the  analysis  that  the  bombs  may  be  sealed  in  the  even- 
ing, so  that  the  heating  may  be  begun  the  first  thing  the  next 


82  GENERAL   PART 

day.  The  sealed  tube  is  kept  under  the  hood  in  the  bomb-room, 
in  the  iron  case,  over  night,  which  is  clamped  with  its  open  end 
directed  vertically  upwards.  The  tube  is  never  allowed  to  remain 
at  the  working  table.  If  the  furnace  is  not  loaded,  naturally  it 
is  most  convenient  to  place  the  bomb  at  once  in  that.  Since  in 
many  cases  the  oxidation  begins  even  at  the  ordinary  temperature, 
pressure  is  developed  in  the  tube ;  therefore,  after  it  has  been 
standing  over  night,  it  must  not  be  removed  from  the  iron  case 
to  be  examined.  The  heating  is  done  gradually ;  at  first,  with 
a  small  flame,  the  gas-tubes  being  lowered  from  the  furnace. 
Gradually  these  are  raised,  and  the  flames  increased  in  size.  The 
following  table  will  show  how  the  heating  of  a  moderately  refractory 
substance  should  be  regulated. 

The  heating  is  begun  at  9  o'clock  A.M. 

From    9-10  the  temperature  is  raised  to  about  100°, 
„  „  „          150°, 


11-12  „  „  „  200, 

12-3  »  »  »          25°°> 

3-6  „  „  „          300°. 

If  an  especially  high  pressure  is  generated  by  the  decomposition 
of  a  substance,  the  danger  of  the  bursting  of  the  tube  may  be 
lessened  by  turning  off  the  gas  before  leaving  the  laboratory  at 
noon,  and  then  in  the  afternoon  opening  the  capillary,  sealing  and 
heating  again  to  a  higher  temperature.  The  same  method  is 
followed  in  working  with  a  substance  so  refractory  that  several 
days'  heating  is  required ;  in  this  case  at  the  beginning  of  the 
second  day  the  pressure  is  reduced  by  opening  the  tube. 

If  two  bombs  are  heated  in  the  furnace  at  the  same  time,  an 
entry  is  made  in  the  note-book  to  show  which  tube  lies  to  the 
right  and  which  to  the  left.  If  this  has  been  neglected,  and  the 
identity  of  the  two  tubes  is  in  doubt,  the  neglect  may  be  corrected 
by  again  weighing  the  two  weighing  tubes. 

To  Open  and  Empty  the  Tube.  —  The  perfectly  cooled  tube  is 
opened  according  to  the  directions  given  on  page  66.  Especial 
care  must  be  taken  before  heating  the  capillary  to  softening  in  a 


ORGANIC  ANALYTICAL   METHODS  83 

large  flame,  to  drive  back  into  the  tube  by  gentle  heating  over  a 
small  flame,  any  of  the  liquid  which  may  have  collected  in  the 
capillary.  Before  the  conical  end  is  broken  off  the  tube  is  exam- 
ined to  see  whether  it  still  contains  crystals  or  oily  drops  of  the 
undecomposed  substance.  In  case  it  does,  the  capillary  is  again 
sealed  and  the  tube  reheated  ;  but  if  it  does  not,  the  conical  end 
is  removed  according  to  the  directions  given  on  page  66.  The 
part  broken  off  is  first  washed  free  from  any  liquid  or  any  of  the 
precipitate  which  may  have  adhered  to  it,  with  distilled  water,  into 
a  beaker ;  the  portion  in  the  tube  is  diluted  with  distilled  water, 
upon  which  there  is  generally  obtained  a  bluish-green  solution, 
coloured  by  nitrous  acid ;  this  is  poured,  together  with  the  weigh- 
ing-tube into  a  beaker  by  inverting  the  tube,  care  being  taken  that 
.the  sudden  falling  of  the  weighing- tube  does  not  break  the  bottom 
of  the  beaker.  In  pouring  out  the  ^tube-contents,  the  attention 
should  be  directed  to  the  open  end  of  the  tube  and  not  to  the 
liquid  in  the  rear  end,  otherwise  some  of  the  liquid  may  easily  be 
spilled.  After  the  outer  open  portion  of  the  tube  has  been  washed 
with  distilled  water  the  tube  is  revolved  and  the  precipitate  in  the 
interior  is  washed  out ;  this  is  repeated  as  often  as  may  be  neces- 
sary. If  a  portion  of  the  silver  halide  adheres  firmly  to  the  glass> 
it  may  be  removed  by  loosening  it  with  a  long  glass  rod  over  the 
end  of  which  has  been  drawn  a  piece  of  rubber  tubing  (such  as  is 
used  in  the  quantitative  analysis  of  inorganic  substances)  and  then 
washing  it  out  with  distilled  water.  The  weighing-tube  is  removed 
from  the  bottom  of  the  beaker  with  a  glass  rod  or  thick  platinum 
wire  held  against  the  walls  above  the  liquid,  washed  thoroughly 
inside  and  out' with  distilled  water,  and  then  raised  with  the  fingers 
and  washed  several  times  again.  At  times  the  weighing-tube  be- 
comes yellow  to  deep  brown  in  colour  due  to  the  formation  of 
silver  silicate.  This  is  not  detrimental  to  the  results  of  the  analysis. 
To  filter  off  and  weigh  the  Silver  Halide.  —  The  beaker  is  now 
heated  on  a  wire  gauze  until  the  silver  halide  has  settled  to  the 
bottom  and  the  supernatant  liquid  is  clear.  Since  the  excess  of 
silver  nitrate  at  times  packs  together  with  the  silver  halide  to  form 
thick,  solid  lumps,  the  precipitate  is  from  time  to  time  crushed 


84  GENERAL  PAR! 

with  a  glass  rod,  the  end  of  which  has  been  flattened  out  to  a  broad 
head.  After  cooling,  the  silver  halide  is  collected  on  a  filter,  the 
weight  of  the  ash  of  which  is  known,  and  washed  with  hot  water 
until,  on  testing  the  filtrate  with  hydrochloric  acid,  no  turbidity 
follows ;  the  filter,  together  with  the  funnel,  is  then  dried  in  an 
air-bath  at  100-110°,  the  funnel  being  covered  with  a  piece  of 
filter-paper.  In  order  to  weigh  the  dry  halide,  as  large  an  amount 
as  possible  is  separated  from  the  paper  carefully,  and  transferred 
to  a  watch-glass  placed  on  a  piece  of  black  glazed  paper.  The 
portions  which  fall  on  the  paper  are  swept  into  the  watch-glass 
with  a  small  feather.  The  filter  is  rolled  up  tightly,  wrapped  with 
a  platinum  wire,  and  ignited  in  the  usual  way  over  a  weighed  por- 
celain crucible  ;  the  heating  is  done  only  with  the  outer  part  of 
the  flame,  and  not  with  the  inner,  reducing  part.  The  folded  filter 
may  also  be  incinerated  directly  in  the  crucible,  which  is  first 
heated  over  a  small  flame,  and  the  temperature  increased  later ; 
the  heating  is  continued  until  the  filter  ash  appears  uniformly 
light.  In  order  to  convert  the  silver  which  has  been  reduced  in 
the  incineration  back  to  the  silver  halide,  the  fused  residue  is 
moistened,  by  the  aid  of  a  glass  rod,  with  a  few  drops  of  nitric 
acid,  —  if  the  latter  method  of  incineration  has  been  employed, 
only  after  complete  cooling  of  the  crucible.  It  is  now  evaporated 
to  dryness  on  the  water-bath.  It  is  then  treated  with  a  few  drops 
of  the  corresponding  halogen  acid,  and  again  evaporated  to  dry- 
ness  on  the  water-bath.  The  principal  mass  of  the  silver  halide 
on  the  watch-glass  is  transferred  to  the  crucible  with  the  aid  of  a 
feather,  and  heated  directly  over  a  small  flame  until  it  just  begins 
to  fuse  :  the  crucible  is  then  placed  in  a  desiccator,  and  allowed  to 
cool.  If  the  analysis  is  intended  to  be  very  exact,  the  principal 
mass  of  the  silver  halide  may  be  moistened  before  fusion,  with  a 
few  drops  of  nitric  acid,  and  then  evaporated  on  the  water-bath 
with  the  halogen  acid. 

The  silver  halide  can  also  be  conveniently  weighed,  either  in  an 
asbestos  tube,  or  in  a  Gooch  crucible.  Concerning  this  compare 
Jannasch, "  Praktischer  Leitfaden  derGewichtsanalyse,"  Second  Ed., 


ORGANIC  ANALYTICAL   METHODS  85 

pages  10  and  145  ;  also  Chemical  News,  37,  181  ;  and  Zeitschrifl 
fur  analytische  Chemie,  19,  333. 

Even  after  taking  the  usual  precautions,  it  sometimes  happens 
that  the  silver  halide  is  mixed  with  fragments  of  glass,  which  will, 
of  course,  cause  the  percentage  of  halogen  to  be  too  high.  If  the 
substance  'under  examination  is  silver  chloride,  and  the  presence 
of  glass  is  noticed  in  the  beaker  or  on  filtering,  an  error  may  be 
avoided,  by  pouring  over  the  completely  washed,  moist  silver 
chloride  on  the  filter,  slightly  warmed  dilute  ammonium  hydroxide 
several  times,  then  washing  the  filter  with  water,  and  precipitating 
the  pure  silver  chloride  in  the  filtrate  by  acidifying  with  hydro- 
chloric acid.  If  the  compound  under  examination  is  silver  bromide 
or  iodide,  and  glass  fragments  have  been  noticed,  the  analysis  is 
carried  out  to  the  end  in  the  usual  way.  To  determine  the  amount 
of  glass  present,  the  silver  halide  in  the  crucible  is  treated  with  very 
dilute  pure  sulphuric  acid,  and  a  small  piece  of  chemically  pure 
zinc  is  added.  In  the  course  of  several  hours,  the  silver  halide  is 
reduced  to  spongy,  metallic  silver.  By  careful  decantation,  the 
liquid  is  separated  from  the  silver,  water  is  added  and  decanted ; 
this  is  repeated  several  times.  It  is  then  treated  with  dilute  nitric 
acid,  and  heated  on  the  water-bath  until  all  the  silver  is  dissolved. 
After  dilution  with  water,  it  is  filtered  through  a  quantitative  filter, 
the  undissolved  glass  fragments  are  also  well  washed  on  the  filter, 
and  the  latter  incinerated.  The  weight  of  the  glass  is  to  be  sub- 
tracted from  the  weight  of  the  halide  obtained.  It  is  obvious  that 
the  purity  of  the  fused  silver  chloride  may  also  be  tested  in  this  way. 

In  conclusion,  the  atomic  weights  of  the  halogens,  the  molecular 
weights  of  the  corresponding  silver  compounds,  and  the  logarithms 
of  the  analytical  constants  are  here  given : 

Cl 
=  3546  ;  AgCl  =  143-34  ;  log  — ^  =  0.39337  -  i 

Br  =  79.92  ;  AgBr  =  187.80  ;  log  =  0.62896  —  i 

1  =  126.92;  Agl    =  234.80;  log  -^-=0.73283  -  i 


86  GENERAL   PART 

Kiister's  Modification.  —  The  determination  of  the  halogens 
may  be  materially  facilitated  by  using  16-20  drops  of  fuming  nitric 
acid  instead  of  iJ-2  c.c.  The  tube  so  charged  is  heated  directly 
up  to  320-340°,  —  it  is  unnecessary  to  heat  it  gradually.  When 
an  ordinary  thermometer  is  employed  to  register  temperatures 
above  300°,  the  column  of  mercury  frequently  parts.  A  bomb- 
thermometer  made  by  C.  Desaga,  Heidelberg,  Germany,  at  the 
suggestion  of  the  author,  corrects  this  defect.  It  contains  nitro- 
gen over  the  mercury  column,  and  possesses  but  two  degree  marks, 
corresponding  to  320°  and  340°. 


QUANTITATIVE  DETERMINATION  OF  SULPHUR 
CARIUS'   METHOD 

This  method,  like  the  preceding  one,  depends  upon  the  com- 
plete oxidation  of  the  weighed  substance,  by  heating  it  with 
fuming  nitric  acid  in  a  sealed  tube.  The  sulphuric  acid  thus 
formed  is  weighed  as  barium  sulphate.  The  charging,  sealing, 
heating,  opening,  and  emptying  of  the  tube  are  performed  in 
exactly  the  same  way  as  in  the  halogen  determinations ;  but  in 
this  case  it  is  evident  that  the  use  of  silver  nitrate  is  superfluous. 
Before  breaking  off  the  conical  end,  the  tube  is  examined  to  see 
that  no  undecomposed  portions  of  the  substance  are  present ;  if 
there  should  be,  the  capillary  is  again  sealed  and  the  tube  re- 
heated. Before  the  sulphuric  acid  is  precipitated  with  barium 
chloride,  the  bottom  of  the  beaker  must  be  examined  for  any 
fragments  of  glass  which  may  be  present ;  if  there  are  any,  they 
are  filtered  off  through  a  small  filter. 

Precipitation  of  the  Barium  Sulphate. — The  liquid  from  the 
bomb,  diluted  with  water  up  to  400  c.c.,  is  heated  almost  to  boiling 
on  a  wire  gauze  and  acidified  with  hydrochloric  acid ;  a  solution 
of  barium  chloride  heated  to  boiling  in  a  test-tube  is  gradually 
added  until  a  precipitate  is  no  longer  formed.  This  can  be  easily 
observed  by  allowing  the  precipitate  to  settle  somewhat  before 
adding  more  of  the  solution.  The  liquid  is  then  heated  over  a 


ORGANIC  ANALYTICAL   METHODS  87 

small  flame  until  the  barium  sulphate  settles  at  the  bottom  of  the 
beaker  and  the  supernatant  liquid  is  perfectly  clear :  at  times 
from  one  to  two  hours'  heating  may  be  necessary.  After  cooling, 
the  liquid  is  filtered,  without  disturbing  the  precipitate  at  the 
bottom,  through  a  small  filter  the  weight  of  the  ash  of  which  is 
known ;  the  precipitate  remaining  in  the  beaker  is  boiled  several 
minutes  with  100  c.c.  water  and  filtered  through  the  same  filter. 
The  precipitate  occasionally  at  first  goes  through  the  paper ;  in 
case  it  does,  another  beaker  is  placed  under  the  funnel  so  that  the 
entire  quantity  of  liquid  need  not  be  refiltered.  The  precipitate 
is  washed  with  hot  water  until  a  portion  of  the  filtrate  tested  with 
dilute  sulphuric  acid  shows  no  turbidity.  Before  throwing  away 
the  filtrate,  barium  chloride  is  added  in  order  to  be  sure  that  a 
sufficient  quantity  was  used  in  the  first  instance.  If  a  precipitate 
is  formed,  the  above  process  is  repeated  and  the  second  precipitate 
collected  on  the  filter  containing  the  first. 

The  method  just  described  has  the  disadvantage  that  if  a 
smaller  quantity  of  water  be  used  for  diluting  the  contents  of  the 
tube  than  that  given  above,  the  barium  sulphate  may  easily  carry 
along  with  it  some  barium  nitrate,  which  is  only  removed  with  diffi- 
culty on  washing  with  water.  Since,  in  consequence  of  this,  the 
percentage  of  sulphur  is  too  high,  it  is  for  many  reasons  preferable 
to  wash  the  contents  of  the  bomb  into  a  porcelain  dish  instead  of 
a  beaker,  and  to  evaporate  the  liquid  on  the  water-bath  until  the 
acid  vapours  vanish,  before  adding  the  barium  chloride ;  by  this 
operation  the  nitric  acid  is  removed.  After  evaporating,  the  res- 
idue is  diluted  with  water,  filtered  if  necessary,  from  any  glass 
fragments,  and  the  operation  just  described  above  repeated. 
Under  these  conditions,  too  much  of  an  excess  of  barium  chloride 
is  to  be  avoided. 

Ignition  and  Weighing  of  the  Barium  Sulphate.  —  In  order  to 
prepare  the  barium  sulphate  for  weighing,  it  is  not  necessary  to 
dry  it  before  incineration ;  if  Bunsen's  method  is  followed,  it  may 
be  incinerated  while  still  moist.  With  the  aid  of  a  small  spatula 
or  knife  the  moist  filter  is  removed  from  the  funnel  and  folded  in 
the  form  of  a  quadrant.  Should  any  barium  sulphate  adhere  to 


88  GENERAL   PART 

the  funnel,  it  is  removed  with  a  small  piece  of  filter-paper,  which 
is  incinerated  with  the  main  mass.  After  the  filter  has  been 
carefully  folded  toward  the  centre,  it  is  pressed  into  the  bottom 
of  a  weighed  platinum  crucible,  placed  on  a  platinum  triangle  in 
such  a  position  that  its  axis  is  inclined  20-30°  from  a  vertical 
position.  The  cover,  also  inclined  at  an  angle  of  20-30°,  in  the 
opposite  direction,  however,  is  supported  before  the  crucible,  so 
that  the  upper  half  of  the  opening  of  the  latter  is  uncovered. 
The  burner  under  the  crucible  is  placed  in  such  a  position  that 
the  flame,  which  must  not  be  too  large  at  first,  is  directly  under 
the  angle  formed  by  the  crucible  and  cover.  This  will  allow  the 
ignition  of  the  filter  to  take  place  at  so  low  a  temperature  that 
reduction  of  the  barium  sulphate  need  not  be  feared.  It  some- 
times happens  that  on  heating  the  filter,  the  gases  formed  take 
fire  at  the  mouth  of  the  crucible,  which,  however,  does  no  harm. 
After  some  time  the  burner  is  placed  under  the  bottom  of  the 
crucible,  the  flame  increased,  and  the  heating  continued  until  the 
residue  has  become  white.  The  crucible  is  now  placed  in  an  up- 
right position,  heated  a  short  time  with  the  full  flame,  and  then 
allowed  to  cool  in  a  desiccator.  It  is  entirely  superfluous  to  treat 
the  barium  sulphate  with  sulphuric  acid  and  then  evaporate  it  off. 
The  barium  sulphate  may  also  be  weighed  in  a  Gooch  crucible. 
(See  page  84.)  If  the  percentage  of  sulphur  found  is  too  high,  this 
may  have  been  caused,  under  certain  conditions,  by  the  fact  that 
in  the  precipitation  too  great  an  excess  of  barium  chloride  has 
been  used,  and  that  the  barium  sulphate  has  carried  along  some  of 
it.  This  source  of  error  may  be  rectified  by  treating  the  ignited 
barium  sulphate  with  water  until  the  crucible  is  half  full,  then  add- 
ing a  few  drops  of  concentrated  hydrochloric  acid,  and  heating  on 
the  water-bath  for  fifteen  minutes.  The  liquid  is  filtered  from  the 
precipitate  through  a  quantitative  filter ;  the  greatest  portion  of 
the  precipitate  remaining  in  the  crucible  is  again  treated  with 
water  and  hydrochloric  acid,  and  the  contents  of  the  crucible 
poured  on  the  filter  already  used ;  after  washing  repeatedly  with 
water,  the  filter  and  precipitate  are  again  ignited  as  before.  This 
process  is  obviously  only  employed  when  the  barium  sulphate  has 


ORGANIC  ANALYTICAL  METHODS  89 

not  been  evaporated  down  with  sulphuric  acid.     For  the  calcula 
tion  of  the  analysis   the  atomic  and  the  molecular  weights  are 

given  : 

g 
S  =  32.07  ;  BaSO4  =  233.44  ;  log  ^          =  0.13792  -  i 

Simultaneous  Determination  of  the  Halogens  and  Sulphur.— 

If  a  substance  contains  both  a  halogen  and  sulphur,  they  may  be 
determined  in  a  single  operation  by  the  following  method  :  As  in 
the  determination  of  the  halogens,  the  bomb  is  charged  with  silver 
nitrate  and  nitric  acid,  and  the  silver  halide  filtered  off  after  the 
heating,  as  above  described.  The  filtrate  thus  obtained  contains, 
besides  the  excess  of  silver  nitrate,  the  sulphuric  acid  formed 
by  oxidation.  This  latter  cannot  be  precipitated  as  before  with 
barium  chloride,  since  the  silver  as  silver  chloride  would  also  be 
thrown  down.  In  its  place  is  used  a  solution  of  barium  nitrate, 
the  purity  of  which  has  been  tested  by  adding  silver  nitrate  to  it. 
The  precipitation  is  made  hot  as  above  directed,  the  solution  used 
being  as  dilute  as  possible  —  the  volume  of  which  must  be  at 
least  500  c.c.  A  large  excess  of  barium  nitrate  is  particularly  to 
be  avoided.  If  the  barium  nitrate  solution  contains  halogen  salts 
as  impurities,  it  is  heated,  and  silver  nitrate  added  so  long  as  a 
precipitate  is  formed,  the  precipitate  filtered  off,  and  the  solution, 
which  is  now  free  from  halogens,  is  used  for  the  precipitation. 


go  GENERAL   PART 


QUANTITATIVE   DETERMINATION   OF   NITROGEN 
DUMAS'  METHOD 

In  scientific  laboratories,  the  method  almost  exclusively  used 
for  determining  nitrogen  quantitatively  is  that  of  Dumas.  The 
principle  involved  is  that  the  substance  is  completely  burned  by 
cupric  oxide  in  a  tube  filled  with  carbon  dioxide,  the  nitrogen  is 
evolved  as  such,  and  its  volume  measured,  while  the  carbon  and 
hydrogen  are  completely  oxidised  to  carbon  dioxide  and  water. 

Requisites  for  the  analysis  : 

1.  A  combustion  tube  of  difficultly  fusible  glass,  80-85  cm-  l°nS  > 

outside  diameter,  about  15  mm. 

2.  A   glass    funnel- tube   with   wide    stem    (at  least    10   mm.   in 

diameter) . 

3.  400  grammes  of  coarse  and  TOO  grammes  of  fine  cupric  oxide. 

The  former  is  kept  in  a  large  flask,  the  latter  in  a  small 
one,  both  of  which  are  closed  by  a  cork  covered  with  tin- 
foil. 

4.  500  grammes  of  magnesite,  in  pieces  the  size  of  a  pea.     The 

fine  powder,  which  cannot  be  used,  is  sifted  out  in  a  wire 
sieve.  The  dark  grains  which  have  become  discoloured 
by  impurities  are  thrown  out. 

5.  A  small  flask  of  pure  methyl  alcohol  (50  grammes)  for  reduc- 

ing the  copper  spiral. 

6.  A  copper  spiral,  10-12  cm.  long.     This  is  made  by  winding 

an  oblong  piece  of  copper  wire  gauze  spirally  around  a 
thin  glass  rod.  It  is  made  of  such  a  width  that  when  in 
position  it  will  touch  the  walls  of  the  combustion  tube ; 
a  space  between  the  walls  and  spiral  is  disadvantageous. 
Also  a  short  copper  spiral  from  1-2  cm.  long. 

7.  A  solution   of  150  grammes  of  potassium  hydroxide  in  150 

grammes  of  water.  It  is  prepared  in  a  porcelain  dish, 
and  not  in  a  glass  beaker  or  flask,  since  these  are  fre- 
quently broken  by  the  heat  generated  by  the  solution. 
After  cooling,  it  is  preserved  in  a  well-closed  bottle. 


ORGANIC  ANALYTICAL   METHODS  9! 

8.  A  nickel  crucible  6  cm.  high ;  diameter  of  top  7  cm.,  for  the 

ignition  of  the  coarse  cupric  oxide. 

9.  A  moderately  large  porcelain  crucible  for  the  ignition  of  the 

fine  cupric  oxide. 
10.   A  small  mortar  with  a  glazed  bottom. 

Besides  these,  a  weighing-tube,  a  one-hole  rubber  stopper  for 
closing  one  end  of  the  combustion  tube,  a  sieve  to  sift  the  copper 
oxide,  a  small  feather,  thermometer,  absorption  apparatus,  and  a 
eudiometer. 

Preparations  for  the  Analysis.  —  The  analysis  is  conveniently 
begun  by  heating  the  entire  quantity  of  coarse  copper  oxide  in 
the  nickel  crucible  over  a  large  flame  (Fletcher  burner),  and 
the  fine  copper  oxide  in  the  porcelain  crucible  over  a  Bunsen 
flame  for  a  long  time,  the  crucibles  being  supported  on  wire  tri- 
angles. The  covers  are  placed  on  the  crucibles  loosely,  and 
the  copper  oxide  occasionally  stirred  with  a  thick  wire.  While 
the  copper  is  being  heated,  one  end  of  the  combustion  tube  is 
sealed  to  a  solid  head,  the  narrower  end  being  selected  for  this 
purpose,  if  the  tube  is  not  perfectly  cylindrical.  The  sealing  is 
done  as  follows  :  The  end  of  the  tube  is  first  warmed  in  a  luminous 
flame,  with  constant  turning ;  it  is  then  heated  to  softening,  in  the 
blast-flame,  a  glass  rod  fused  on  it,  and  the  heated  portion  suddenly 
drawn  out  to  a  narrow  tube.  The  glass  rod  is  now  fused  off,  and 
the  conical  part  of  the  tube  just  produced  is  heated  and  drawn 
out.  The  cone  is  then  heated  in  the  hottest  flame  until  it  falls 
together ;  it  is  finally  allowed  to  cool  gradually  over  a  small 
luminous  flame.  When  this  operation  is  finished,  the  open  end 
of  the  tube  is  warmed  in  a  luminous  flame,  and,  with  constant 
turning,  the  sharp  edges  are  rounded  by  the  blast-flame  :  it  is  then 
allowed  to  cool  in  the  luminous  flame  again.  After  complete 
cooling,  the  soot  is  removed,  the  tube  rinsed  out  several  times 
with  water,  the  water  allowed  to  drain  off  as  completely  as  possible, 
and  the  tube  finally  dried  in  one  of  the  two  following  ways  :  The 
tube,  with  constant  turning,  is  repeatedly  passed  through  the  large 
luminous  flame  of  a  blast-lamp,  while  a  current  of  air  is  blown 


92  GENERAL  PART 

from  a  blast  into  the  bottom  of  it  by  means  of  a  narrower,  longer 
(10  cm.)  tube  inserted  in  the  larger  tube;  this  operation  is  con- 
tinued until  all  moisture  is  removed.  Or  the  combustion  tube  is 
clamped  in  a  horizontal  position,  a  narrower  tube  extending  to 
the  sealed  end,  attached  to  suction,  is  inserted,  and  the  combustion 
tube  equally  heated  with  a  Bunsen  burner  throughout  its  entire 
length ;  the  water  vapour  is  drawn  off  by  the  suction.  To  reduce  the 
long  copper  spiral  which  is  to  be  used  for  the  reduction  of  oxides 
of  nitrogen  which  may  be  formed,  the  method  of  procedure  is  as 
follows  :  Into  a  test-tube  large  enough  to  admit  the  spiral,  i  c.c.  of 
methyl  alcohol  is  placed  ;  the  spiral,  held  by  crucible  tongs,  is  then 
heated  to  glowing  in  a  large,  somewhat  roaring  blast-flame,  and 
dropped  as  quickly  as  possible  into  the  test-tube ;  since  this  be- 
comes strongly  heated  at  its  upper  end,  it  is  clamped  in  a  test-tube 
holder,  or  wrapped  in  a  cloth  or  strips  of  paper.  The  dark  spiral 
soon  assumes  a  bright  metallic  lustre,  while  vapours,  having  a  sharp, 
pungent  odour  (oxidation  products  of  methyl  alcohol  like  formic 
aldehyde  and  formic  acid),  which  frequently  become  ignited,  are 
formed ;  after  a  few  minutes,  the  tube  may  be  loosely  corked,  and 
the  spiral  allowed  to  cool.  When  this  operation  is  ended,  the  cop- 
per oxide  will  have  been  sufficiently  heated,  and  the  flames  may  be 
removed.  During  the  cooling,  the  substance  to  be  analysed  is 
weighed.  A  convenient  method  is  this  :  The  weight  of  the  weigh- 
ing-flask is  determined  with  exactness  to  centigrammes,  this  weight 
is  entered  in  the  note-book  at  a  convenient  place  for  future  use. 
The  substance  to  be  analysed  is  now  placed  in  the  weighing-tube, 
and  the  weight  of  the  tube,  plus  substance,  is  determined  exactly 
to  the  tenth  of  a  milligramme.  In  the  meantime,  the  copper 
oxide  has  cooled  sufficiently  to  be  transferred  to  the  appropriate 
flask.  The  combustion  tube  is  next  filled. 

Filling  the  Tube.  — At  the  edge  of  the  working  table  is  placed 
a  stand ;  fastened  firmly  near  the  bottom  of  this  is  a  clamp  pro- 
jecting over  the  edge  of  the  table  supporting  the  combustion  tube 
in  a  vertical  position,  the  mouth  being  at  about  the  level  of  the 
table.  The  tube  is  now  directly  filled  with  the  magnesite  until 
the  layer  has  a  height  of  10-12  cm.  (Fig.  54).  A  small  roll  of 


ORGANIC  ANALYTICAL   METHODS 


93 


30  cm.  coarse  oxide 


copper  gauze  1-2  cm.  long,  held  with  pincers  or  tongs,  is  heated 
for  a  short  time  in  a  Bunsen  flame  (it  need  not  be  reduced)  and 
dropped  on  the  magnesite.  The  funnel- tube  is  then  placed  in 
the  tube,  and  from  the  flask  coarse  copper  oxide  is  poured  in  until 
the  layer  measures  8  cm.,  and  upon  this  is  poured  a  layer  of  2  cm. 
of  the  fine  oxide.  To  the  operation  following  —  the  mixing  of  the 

substance  with  copper  oxide 
s  cm.  free  and  the  transference  of  the 

mixture  to  the  tube  —  especial 

10  cm.  reduced  copper  spiral         care    must    be    given.       In    the 

bottom  of  a  small  mortar, 
standing  on  black,  glazed  pa- 
per a  ^  cm.  layer  of  the  fine, 
perfectly  cooled  copper  oxide 
is  placed ;  to  this  is  added  from 
the  weighing- tube  the  sub- 
stance to  be  analysed,  of  which 
0.15-0.20  gramme  is  taken, 
unless  the  substance  contains 
a  small  proportion  of  nitrogen, 
when  more  is  taken.  Since 
the  weight  of  the  empty  tube 
is  known  as  well  as  that  of 
the  substance  contained  there- 
in, one  can  easily  decide,  by 
measuring  with  the  eye,  how 
much  of  the  substance  to 
take.  Fine  copper  oxide  is 
now  added  until  the  substance 
is  completely  covered,  and  the 
two  are  carefully  mixed  by 
stirring  with  the  pestle,  without  pressure  ;  during  the  mixing  care 
must  be  taken  not  to  stir  so  rapidly  as  to  cause  dust-like  particles 
of  the  mixture  to  leave  the  mortar.  With  the  aid  of  a  clean, 
clipped  feather,  such  as  is  used  in  quantitative  operations,  or  a 
small  brush,  the  contents  of  the  mortar  are  transferred  through 


10  cm.  substance  +  fine  oxide 


2  cm.  fine  oxide 


8  cm.  coarse  oxide 


;m.  copper  spiral 


12  cm.  magnesite 


FIG.  54. 


94  GENERAL   PART 

the  funnel-tube  into  the  combustion  tube.  The  operation  must  be 
done  cautiously  to  prevent  the  light,  dusty  particles  from  being 
blown  away.  The  mortar,  as  well  as  the  pestle,  is  now  rinsed 
with  a  fresh  portion  of  the  fine  copper  oxide,  and  this  is  likewise 
transferred  to  the  tube  with  the  aid  of  the  feather.  The  layer  of 
substance  plus  copper  oxide  should  be  about  10  cm.  long.  Then 
follows  a  layer  of  30  cm.  of  coarse  copper  oxide,  and  finally  the 
reduced  copper  spiral. 

The  length  of  the  tube,  as  well  as  that  of  the  single  layers,  is 
regulated  in  accordance  with  the  size  of  the  combustion  furnace ; 
the  figures  given  above  refer  to  a  furnace  possessing  a  flame  surface 
of  75  cm.  Generally  the  tubes  are  5  cm.  longer  than  the  furnace  ; 
the  tube  contents  are  of  the  same  length  as  the  flame  surface. 

Heating  the  Tube.  —  After  the  tube  is  filled  it  is  held  in  a  hori- 
zontal position  and  tapped  gently  on  the  table  in  order  that  a 
canal  may  be  formed  in  the  upper  portion  of  the  fine  copper 
oxide ;  it  is  then  connected  with  a  rubber  stopper  to  the  absorp- 
tion apparatus  which  has  been  charged  with  caustic  potash  solution, 
and  placed  in  the  combustion  furnace,  the  rear  end  of  which  (that 
under  the  magnesite)  has  been  raised  on  a  block  (Fig.  55).  The 
following  points  are  to  be  observed  :  In  the  lower  part  of  the 
absorption  apparatus  there  must  be  a  sufficient  amount  of  mercury 
to  extend  almost  to  the  side-tube ;  if  this  is  not  the  case,  more  mer- 
cury is  added :  the  end  of  the  glass  tube  passing  through  the 
rubber  stopper  must  be  flush  with  the  end  of  the  stopper.  In 
order  to  protect  the  latter  from  the  heat,  there  is  placed  over  the 
portion  of  the  tube  projecting  beyond  the  furnace,  an  asbestos 
plate  having  a  circular  opening  in  the  centre.  After  opening  the 
pinch-cock  of  the  absorption  apparatus,  the  burners  under  the  last 
half  of  the  magnesite  are  lighted ;  the  flames,  being  small  at  first, 
are  increased  in  size,  as  soon  as  the  tube  becomes  warmed,  but  not 
sufficiently  to  cause  them  to  meet  above  the  tube.  In  order  to 
raise  the  temperature  higher  when  it  becomes  necessary,  the  tube 
is  covered  from  both  sides  with  the  tiles.  After  about  ten  minutes 
a  rapid  current  of  carbon  dioxide  is  evolved,  the  magnesite  being 
decomposed  by  heat  as  represented  in  the  following  equation : 


ORGANIC  ANALYTICAL   METHODS 


96  GENERAL   PART 

During  this  operation  the  glass  stop-cock  of  the  absorption  appa- 
ratus is  opened,  and  the  pear-shaped  vessel  placed  as  low  as  pos- 
sible, so  that  it  contains  the  principal  portion  of  the  caustic  potash. 
After  a  rapid  current  of  carbon  dioxide  has  been  evolved  for  about 
fifteen  minutes,  the  burners  under  the  copper  spiral  are  lighted 
in  order  to  drive  out  any  occluded  gas  (hydrogen),  the  pear- 
shaped  vessel  is  raised  high  enough  to  cause  the  caustic  potash 
to  ascend  somewhat  above  the  tubulure  in  the  glass  cock,  the 
latter  is  closed,  and  the  pear-shaped  vessel  again  lowered  as  far 
as  possible.  When  the  air  in  the  tube  has '  been  completely 
replaced  by  carbon  dioxide,  only  a  minimum  quantity  of  light 
foam  should  collect  over  the  potash  in  the  course  of  two  minutes. 
If  this  is  not  the  case,  and  a  large  air  volume  collects,  the  glass 
cock  is  opened,  upon  which  the  potash  flows  in  to  the  lowered 
pear  vessel,  and  carbon  dioxide  is  caused  to  pass  through  the 
tube  for  five  minutes  longer.  The  pear  vessel  is  then  raised  as 
high  as  at  first,  the  glass  cock  closed,  and  the  former  lowered.  An 
observation  will  show  whether  the  air  has  been  displaced,  which 
should  be  the  case  under  normal  conditions.  If  now  after  two 
minutes  only  a  trace  of  foam  has  collected,  the  end  of  the  delivery 
tube  is  dipped  under  the  water  in  a  dish  as  shown  in  Fig.  55,  the 
pear  raised  to  the  highest  point  of  the  delivery  tube,  and  the  glass 
cock  opened  in  order  that  the  potash  may  drive  out  the  air  in  the 
delivery  tube  :  when  this  has  been  done,  the  cock  is  closed  again 
and  the  pear  lowered  to  the  bottom.  All  the  flames  but  one 
under  the  magnesite  are  now  extinguished  or  lowered,  and  those 
under  the  long  copper  spiral  as  well  as  those  under  four-fifths  of 
the  adjacent  layer  of  coarse  copper  oxide  are  lighted  at  the  same 
time  ;  the  flames,  small  at  first,  are  increased  in  size,  after  the  tube 
has  become  somewhat  heated,  until  the  copper  oxide  is  heated 
to  dull  redness.  Concerning  the  steps  taken  in  heating  the  tube, 
refer  to  Fig.  54  —  the  numbers  on  the  left  indicate  the  portions  of 
the  tube  to  be  heated  successively.  At  .this  point  care  is  taken 
that  the  flames  are  not  so  large  as  to  meet  above  the  tube.  As 
before  in  heating  the  magnesite,  after  the  first  warming  the  heated 
portions  of  the  tube  are  covered  on  both  sides  with  the  tiles.  As 
soon  as  the  forward  layer  of  coarse  copper  oxide  becomes  dark 
red,  the  burners  under  the  rear  layer  of  coarse  oxide  adjacent  to 


ORGANIC  ANALYTICAL  METHODS  97 

the  magnesite  are  lighted  —  small  flames  at  first,  which  are  increased 
after  a  time,  the  tube  being  covered  simultaneously  with  the  tiles. 
Care  must  be  taken  that  the  flames  nearest  the  layer  of  substance 
plus  fine  copper  oxide  are  not  too  large,  in  order  that  the  substance 
may  not  yet  be  burned.  Upon  the  operation  which  now  follows — 
the  gradual  heating  of  the  fine  oxide  containing  the  substance  — 
virtually  depends  the  success  of  the  analysis.  For  the  proper 
manipulation  of  this  operation  especial  care  must  be  taken.  It  is 
a  rule  that  the  heating  had  better  be  somewhat  too  slow  than  too 
rapid.  A  small  flame  is  now  lighted  at  the  point  adjacent  to  the 
short  layer  of  coarse  oxide  :  an  observation  of  the  absorption  appa- 
ratus will  show  whether  after  some  time  any  unabsorbed  gas  collects. 
If  this  is  the  case,  no  other  burners  are  lighted  until  the  evolution 
of  gas  ceases.  When  the  gas  no  longer  collects,  another  burner 
on  the  opposite  side  of  the  fine  oxide  is  lighted.  In  this  way  the 
burners  are  gradually  lighted  from  both  sides,  toward  the  middle 
of  the  fine  oxide,  and  after,  in  each  case,  the  cessation  of  the 
evolution  of  the  gas,  the  flames  are  gradually  made  larger  until 
finally  the  tube  covered  with  tiles  is  heated  with  full  flames ;  thus 
the  substance  is  regularly  and  quietly  burned.  The  combustion 
must  be  so  conducted  that  the  bubbles  of  gas  ascend  in  the  absorp- 
tion apparatus  with  a  slow  regularity.  If  the  single  bubbles  cannot 
be  counted,  or  if  they  are  so  large  as  to  occupy  almost  the  entire 
cross-section  of  the  absorption  tube,  the  heating  is  too  strong,  and 
the  last  burners  lighted  must  be  extinguished  or  lowered,  the  tiles 
being  also  laid  back  at  the  same  time  if  necessary,  until  the  gener- 
ation of  the  gas  is  lessened.  When  this  is  ended,  small  flames  are 
again  lighted  under  the  entire  layer  of  magnesite,  and  increased  in 
size  after  some  time.  As  soon  as  the  evolution  of  carbon  dioxide 
has  become  active,  the  flames  under  the  rear  half  of  the  magnesite 
lighted  at  the  beginning  of  the  analysis  are  extinguished.  After  a 
rapid  current  of  carbon  dioxide  has  passed  through  the  tube  for 
ten  minutes,  all  the  nitrogen  is  carried  over  to  the  absorption 
apparatus.  This  is  shown  by  the  complete  absorption  of  the  gas 
bubbles  by  the  potash,  as  at  the  beginning  of  the  analysis,  except 
for  a  minimum  foam-like  residue.  The  absorption  apparatus  is 
H 


98 


GENERAL  PART 


then  closed  by  the  pinch- cock  and  the  rubber  stopper  bearing  tha 
connecting  tube  is  withdrawn  from  the  combustion  tube.  The  gas 
is  not  immediately  transferred  to  the  eudiometer,  but  the  pear  is 
raised  until  the  surfaces  of  the  liquid  in  the  pear  and  that  in  the 
tube  are  at  the  same  level :  the  apparatus  is  then  allowed  to  stand 
for  at  least  half  an  hour.  The  flames  under  the  combustion  tube 
are  not  turned  out  simultaneously,  but  first  one  is  extinguished, 
and  then  after  a  short  time  another,  and  so  on.  During  the  cool- 
ing of  the  tube  the  weighing-flask  is  weighed  again. 

Transferring  the  Nitrogen.  —  After  the  nitrogen  has  stood  in 
contact  for  at  least  half  an  hour  with  the  caustic  potash,  in  order 
that  the  last  portions  of  carbon 
dioxide  may  be  absorbed,  the 
end  of  the  delivery  tube  is  dipped 
under  the  surface  of  the  water 
contained  in  a  wide-mouth  cylin- 
der, as  represented  in  Fig.  56, 
care  being  taken  that  in  the 
lower  bent  portion  of  the  de- 
livery tube  no  air  bubbles  are 
present ;  if  there  are,  they  must 
be  removed  with  a  capillary 
pipette.  The  eudiometer  is  now 
filled  with  water,  the  end  closed 
with  the  thumb,  inverted  and 
dipped  below  the  surface  of  the 

r  IG.  50. 

water,  the   thumb  removed  and 

the  tube  clamped  to  the  cylinder,  at  an  oblique  angle,  so  that  the 
end  of  the  delivery  tube  may  be  passed  under  it.  The  pear 
supported  by  the  clamped  ring  is  raised  as  high  as  possible  above 
the  delivery  tube,  and  the  glass  cock  gradually  opened.  The 
nitrogen  is  thus  transferred  to  the  eudiometer,  the  cock  being 
left  open  until  the  delivery  tube  is  completely  filled  with  the 
caustic  potash.  The  absorption  apparatus  is  then  removed,  the 
eudiometer  wholly  immersed  in  the  water.  To  obtain  the  tem- 
perature, a  thermometer,  held  in  the -clamp  which  supported  the 


ORGANIC  ANALYTICAL  METHODS  99 

delivery  tube,  is  immersed  in  the  water  as  far  as  possible.  After 
about  ten  minutes,  the  nitrogen  has  come  to  the  same  tempera- 
ture as  the  water,  the  eudiometer  is  then  seized  with  a  clamp 
especially  adapted  to  this  purpose,  or  crucible  tongs,  —  never  with 
the  hands,  —  and  is  raised  so  far  out  of  the  water  that  the  level 
of  water  inside  and  outside  the  tube  is  the  same.  The  volume  of 
gas  thus  read  off,  is  under  the  same  pressure  as  that  indicated  by 
a  barometer. 

Calculations  of  the  Analysis.  —  If  s  is  the  amount  of  substance 
in  grammes,  v  the  volume  of  nitrogen  read  at  the  temperature  /°, 
and  b  the  height  of  the  barometer  in  millimetres,  w  the  tension 
of  the  water  vapour  in  millimetres  at  /°,  then  the  percentage  of 
nitrogen  is  p  : 

_      v  •  (b  —  w)  •  0.12505 

~~  760  •  (i  +  0.00367  •  /)  •  s' 

The  calculation  of  the  analysis  is  rendered  easier  by  referring  to 
the  table  in  which  the  weight  of  one  cubic  centimetre  of  moist 
nitrogen  is  given  in  milligrammes  at  different  temperatures  and 
pressures.  If  this,  under  the  observed  conditions,  is  g,  then  the 
percentage  of  nitrogen  is  : 

100  XVX 


In  this  formula,  s  is  the  weight  of  the  substance  in  milligrammes. 

A  table  is  given  at  the  end  of  the  book  for  these  calculations. 
The  values  for  the  height  of  the  barometer  not  found  in  the  table 
may  be  obtained  by  interpolation.  For  ordinary  work  it  is 
unnecessary  to  read  off  fractions  of  degrees  on  a  thermometer, 
or  of  millimetres  on  a  barometer,  since  the  slight  differences  in 
values  found  in  this  manner  lie  within  the  limits  of  experimental 
error. 

The  upper  figure  in  each  space  in  the  table  is  the  weight  of 
moist  nitrogen  in  milligrammes,  and  the  lower  figure  is  the  mantissa 
of  the  logarithm  of  the  weight  of  nitrogen. 

Length  of  Time  for  an  Analysis.  —  The  following  abstract  will 
give  an  approximate  iclea"  of  '  the  length  of  time  that  the  single 


100  GENERAL   PART 

operations  of  a  well-conducted  cpmbustion  ought  to  occupy. 
From  the  beginning  of  the  heating  of  the  magnesite  to  the  ap- 
pearance of  a  rapid  current  of  carbon  dioxide  requires  about 
10  minutes,  the  first  test  as  to  whether  air  is  still  present  in  the 
tube  follows  after  a  further  15  minutes ;  length  of  time  for  various 
tests,  5  minutes.  From  the  warming  of  the  forward  layer  of  the 
copper  oxide  with  the  spiral  to  the  heating  of  the  rear  layer  of 
oxide  to  a  dark  red  heat,  15  minutes.  The  actual  combustion 
of  the  substance  requires  30  minutes.  The  displacement  of  the 
last  portions  of  nitrogen  by  heating  the  magnesite  requires  10 
minutes.  Total,  i  hour  and  25  minutes. 

These  time  figures  are,  of  course,  only  to  be  considered  as 
approximate,  since  they  depend  upon  the  efficiency  of  the  fur- 
nace, upon  the  nature  of  the  substance  burned,  upon  the  skill 
of  the  experimenter,  and  upon  other  factors. 

Subsequent  Operations.  —  After  the  tube  has  cooled  and  the 
copper  spiral  taken  out,  all  the  copper  oxide  is  sifted  to  separate 
the  coarse  from  the  fine,  and  may  be  used  again  for  further 
analyses  as  often  as  desired,  provided  that  it  is  reheated  each 
time  in  the  nickel  crucible  to  oxidise  it.  The  tube  may  also  be 
used  again  if  it  has  not  been  distorted  by  high  heating.  The 
magnesite  is  useless  for  further  analyses. 

The  caustic  potash  in  the  absorption  apparatus,  which  can  be 
used  a  second  time,  is  poured  into  a  bottle,  which  is  then  well 
closed.  The  absorption  apparatus,  including  the  rubber  tubing,  is 
washed  out  repeatedly  with  water,  so  that  the  latter  may  not  be 
corroded  by  the  caustic  potash. 

General  Remarks.  —  The  above-described  method  of  Dumas 
for  nitrogen  is  used  in  variously  modified  forms,  but  the  principle 
is  the  same  in  all.  It  is  preferred  in  many  places  to  generate  the 
carbon  dioxide  from  acid  sodium  carbonate  or  manganese  car- 
bonate. A  combustion  tube  open  at  both  ends  may  be  used,  if  a 
number  of  nitrogen  determinations  are  to  be  made.  The  tube 
is  charged  as  represented  in  Fig.  60  (page  107).  The  substance 
is  placed  in  a  porcelain  or  copper  boat.  In  order  to  replace  the 
air  by  carbon  'dioxide,  t're  fear 'end1  of  the'tuBe  'is  connected  with 


ORGANIC   ANALYTICAL   METHODS  IOI 

another  tube  of  difficultly  fusible  glass  (closed  at  one  end),  25-30 
cm.  long  and  15-20  ram.  wide,  which  is  three-fourths  filled  (in 
cross  section)  with  sodium  bicarbonate.  In  order  to  absorb  the 
water  generated  from  this  on  heating,  a  small  sulphuric  acid  wash 
bottle  is  interposed  between  the  two  tubes.  The  layer  of  bicar- 
bonate is  heated  with  a  single  Bunsen  burner,  beginning  at  the 
fused  end.  In  order  to  protect  the  bicarbonate  tube  from  the 
direct  flame,  it  is  surrounded  by  a  cylinder  of  coarse  iron  gauze 
(Fig.  57).  The  bicarbonate  may  be  replaced  by  a  Kipp  generator. 
Further,  the  mixing  of  the  substance  with  the  fine  copper  oxide 
may  be  done  in  the  tube.  Instead  of  the  absorption  apparatus 


FIG.  57. 


of  Schiff,  described  above,  a  graduated  tube  from  which  the  vol- 
ume of  the  gas  may  be  read  directly  may  be  used,  thus  obviating 
the  necessity  of  transferring  it  to  a  eudiometer.  This  modifica- 
tion carries  with  it,  however,  the  disadvantage  that  the  tension  of 
caustic  potash  is  not  exactly  known,  and  therefore  a  somewhat 
arbitrary  correction  must  be  applied.  But  as  mentioned  these 
modifications- do  not  differ  essentially. 


QUANTITATIVE  DETERMINATION   OF   CARBON  AND  HYDROGEN 
LIEBIG'S  METHOD 

The  essential  part  of  the  method  consists  in  completely  burning 
with  copper  oxide  a  weighed  amount  of  the  substance,  and  then 
weighing  the  combustion  products,  carbon  dioxide  and  water. 

The  requisites  for  analysis  are  : 


102  GENERAL  PART 

1.  A  hard  glass  tube  open  at  both  ends;  outside  diameter  12- 

15  mm.     It  should  be  about  10  cm.  longer  than  the  furnace. 

2.  Four  hundred  grammes  of  coarse  and  50  grammes  of  fine 

copper  oxide,  preserved  in  bottles  closed  with  tin-foil- 
covered  corks  as  in  the  nitrogen  determination.  But  the 
copper  oxide  used  for  the  latter  purpose  and  that  for  the 
carbon  and  hydrogen  determinations  are  always  kept  in 
separate  bottles. 

3.  A  U-shaped  and  a  straight  calcium  chloride  tube. 

4.  A  caustic  potash  apparatus.     The  Geissler  form  is  the  most 

convenient. 

5.  A  drying  apparatus  for  air  or  oxygen. 

6.  Two  one-hole  rubber  stoppers  fitting  the  ends  of  the  com- 

bustion tube. 

7.  A  glass  tube  provided  with  a  cock. 

8.  Two  copper  spirals  of  10  and  12-15  cm-  length,  respectively  ; 

two  short  spirals  1-2  cm.  long. 

9.  A  piece  of  good  rubber  tubing  20  cm.  long ;  six  pieces  rubber 

tubing  2  cm.  long  (thick-walled  and  seamless). 

10.  A  porcelain  and  a  copper  boat. 

11.  A  screw  pinch-cock. 

12.  Two  asbestos  plates  for  the  protection  of  the  rubber  stoppers. 

Preparations  for  the  Analysis.  —  The  sharp  edges  of  the  com- 
bustion tube  are  rounded  by  careful  heating  in  a  blast-flame.  After 
cooling  the  tube  is  rinsed  out  with  water  several  times ;  this  is 
allowed  to  drain  off,  and  the  tube  dried  by  one  of  the  methods 
given  on  pages  91  and  92. 

The  coarse  copper  oxide  is  not  previously  heated  in  the  nickel 
crucible  as  in  the  determination  of  nitrogen,  but  this  is  done  later 
in  the  tube  itself.  If  the  nature  of  the  substance  to  be  analysed 
is  such  that  it  is  necessary  to  mix  it  with  fine  copper  oxide,  the 
latter  is  ignited  for  a  quarter  hour  in  the  porcelain  crucible  and 
allowed  to  cool  in  a  desiccator. 

The  U-tube  for  the  absorption  of  the  water  (Fig.  61)  is  filled 
with  granulated,  not  fused,  calcium  chloride,  which  must  be  freed 


ORGANIC  ANALYTICAL   METHODS  1 03 

from  any  powder  by  sifting.  In  order  to  prevent  the  calcium 
chloride  from  falling  out,  both  ends  of  the  tube  are  provided  with 
loose  plugs  of  cotton.  The  open  leg  is  closed  by  a  rubber  stopper 
or  a  good  cork  bearing  a  glass  tube  bent  at  a  right  angle.  The 
cork  stopper  is  covered  with  a  thin  layer  of  sealing-wax.  Calcium 
chloride  tubes,  in  which  the  open  leg  is  longer  than  the  other,  are 
very  convenient.  After  the  tube  is  filled  the  open  end  may  be 
sealed  in  a  blast-flame.  In  this  case  the  plug  in  this  end  is  not 
cotton,  but  asbestos  or  glass-wool.  In  order  that  the  tube  may 
be  suspended  from  the  arm  of  the  balance  in  weighing,  a  platinum 
wire  with  a  loop  in  the  centre  is  attached  to  both  legs.  Calcium 
chloride  often  contains  basic  chlorides,  which  not  only  absorb 
water,  but  also  carbon  dioxide,  thus  causing  an  error  in  the  results 
of  the  analysis ;  before  the  filled  tube  is  used  a  stream  of  dry 
carbon  dioxide  is  passed  through  it  for  about  two  hours,  dried  air 
is  then  drawn  through  for  half  an  hour  to  displace  the  carbon 
dioxide.  The  two  side  tubes  of  the  calcium  chloride  tube  are 
closed  by  pieces  of  rubber  tubing  2  cm.  long,  in  which  is  inserted 
a  glass  rod  rounded  at  both  ends,  i|  cm.  long.  The  tube  may 
be  used  repeatedly  until  the  calcium  chloride  begins  to  liquefy. 
The  straight  calcium  chloride  tube  is  filled  in  like  manner,  but  it 
is  unnecessary  to  pass  carbon  dioxide  through  this  before  using. 

The  three  bulbs  of  the  potash  apparatus  similar  to  the  one 
represented  in  Fig.  58  are  three-fourths  filled  with  a  solution  of 
caustic  potash  (2  parts  potassium  hydroxide,  3  parts  water)  as 
follows  :  the  horizontal  tube  which  is  to  be  charged  with  solid 
caustic  potash  is  removed,  and  to  the  free  end  of  the  bulb  tube 
rubber  tubing  is  attached.  The  inlet  tube  represented  in  Fig.  58 
at  the  left  is  now  dipped  into  the  caustic  potash  solution,  con- 
tained in  a  shallow  dish,  and  this  is  sucked  up  with  the  rubber  tub- 
ing until  the  three  bulbs  are  three-fourths  filled.  Care  must  be 
taken  not  to  suck  too  strongly,  otherwise  some  of  the  caustic  potash 
solution  may  be  drawn  into  the  mouth.  This  may  be  prevented  by 
inserting  an  empty  wash  bottle  between  the  potash  apparatus  and 
the  n  outh,  or  the  suction-pump  may  be  used,  in  which  case  the 
watei  -cock  must  be  opened  to  a  very  slight  extent.  After  filling 


104  GENERAL    PART 

the  bulbs  that  part  of  the  tube  immersed  in  the  potash  solution 
is  cleaned  with  pieces  of  rolled-up  filter-paper.  The  horizontal 
potash  tube,  removed  before  filling  the  bulbs,  is  now  filled  with 
coarse-grained  soda-lime  and  solid  caustic  potash  in  pea-size 
pieces  as  follows  :  In  the  bulb  is  placed  a  plug  of  glass-wool  or 
asbestos,  then  follows  a  layer  of  the  soda-lime,  a  layer  of  caustic 
potash,  and  finally  another  plug  of  glass-wool  or  asbestos.  When 
this  is  done,  it  is  closed  in  the  same  way  as  the  calcium 
chloride  tube.  In  handling  the  Geissler  tubes  it  is  always  to  be 
remembered  that  they  are  very  fragile,  and  in  all  cases  the  lever- 


FlG.  58. 

arm  formed  in  lifting  them  should  be  as  short  as  possible.  When 
the  apparatus  is  to  be  closed  by  rubber  tubing,  e.g.,  it  is  not 
grasped  by  the  bulbs,  but  immediately  behind  the  place  over 
which  the  tubing  is  to  be  drawn  or  pushed.  When  the  potash 
apparatus  has  been  used  twice,  it  must  be  refilled.  The  longer  of 
the  two  so-called  copper  oxide  spirals  need  not  be  reduced  before 
the  combustion  ;  on  the  contrary,  it  is  oxidised  in  the  combustion 
tube,  as  will  be  pointed  out  below.  In  order  to  be  able  to  remove 
it  from  the  tube  conveniently  a  loop  of  copper  wire  is  fastened  in 
the  meshes  of  the  gauze  near  the  end,  or  a  not  too  thin  copper 
wire  is  passed  through  the  centre  of  the  spiral  and  bent  at  one 
end  to  a  right  angle  and  at  the  other  in  the  form  of  a  loop.  The 


ORGANIC  ANALYTICAL   METHODS 


105 


shorter  spiral,  which,  as  in  the  nitrogen  determination,  serves  to 
reduce  any  oxides  of  nitrogen,  is  next  reduced  according  to  the 
directions  given  on  page  92.  To  remove  any  adhering  organic 
substances  like  methyl  alcohol  or  its  oxidation  products  the  spiral 
is  placed,  after  cooling,  in  a  glass  tube  20  cm.  long,  one  end  of 
which  is  narrowed ;  carbon  dioxide  is  passed  through  it,  and  as 
soon  as  the  air  has  been  displaced,  it  is  heated  for  a  few  minutes 
with  a  Bunsen  flame  and  then  allowed  to  cool  in  a  current  of  car- 
bon dioxide.  To  remove  the  mechanically  adhering  gas  the  spiral 
is  placed  in  a  vacuum  desiccator.  If  this  is  not  at  hand,  an  ordi- 
nary desiccator  containing  a  small  dish  of  solid  caustic  potash  or 
unslaked  lime  is  used.  (It  may  also  be  heated  in  an  air-bath  at 
loo-no0.) 

For  drying  the  oxygen  or  air  an  apparatus  consisting  of  two  wash 
cylinders  and  two  U-shaped  glass  tubes  mounted  on  a  wooden 
stand  is  employed.  The  gas  passes  first 
through  a  wash  cylinder  containing  a 
solution  of  potassium  hydroxide  (i  :  i), 
then  a  tube  filled  with  soda-lime,  then 
one  filled  with  granulated  calcium  chlo- 
ride, and  finally  a  wash  cylinder  contain- 
ing sulphuric  acid  (Fig.  59). 

The  legs  of  the  glass  tube  containing 
the  stop-cock  are  fused  off  and  slightly 
narrowed  at  the  ends,  so  that  on  either 
side  of  the  cock  the  length  is  5  cm. 

Filling  the  Tube. — The  simplest  case 
of  combustion  with  which  one  can  deal 
is  that  involving  the  analysis  of  a  sub- 
stance containing  no  nitrogen.  In  a 
case  of  this  kind,  assuming  that  the  furnace  has  a  flame  surface 
of  75  cm.,  the  tube  is  filled  in  the  following  manner :  A  short 
copper  gauze  roll,  1-2  cm.  long,  of  sufficient  diameter  to  fit  the 
tube  tightly,  and  somewhat  elastic,  is  pushed  into  the  tube  5  cm., 
and  then  the  opposite  side  of  the  tube  is  partially  filled  with  a 
layer  of  coarse  copper  oxide  45  cm.  held  in  position  by  another 


FIG.  59. 


I06  GENERAL   PART 

small  elastic  copper  spiral  at  its  upper  end.  Into  the  tube  lying 
in  a  horizontal  position  the  copper  oxide  spiral  is  pushed  so  far 
that  its  loop  is  5  cm.  from  the  mouth  of  the  tube  (Fig.  60). 

Igniting  the  Copper  Oxide.  —  The  charged  tube  is  placed  in  the 
furnace,  the  end  nearest  the  copper  oxide  spiral  is  closed  by  a 
rubber  stopper  bearing  the  glass  stop-cock  tube,  and  the  latter  is 
connected  with  the  drying  apparatus  by  means  of  rubber  Jtubing 
provided  with  a  screw  pinch-cock.  The  other  end  of  the  tube 
is  allowed  to  remain  open  at  first ;  while  a  current  cf  oxygen  is 
passed  through  the  tube,  slow  enough  to  enable  one  to  count  the 
bubbles  (the  glass  stop-cock  is  opened  wide  and  the  current  regu- 
lated with  the  pinch-cock),  the  entire  length  of  the  tube  is  heated, 
at  first  with  flames  as  small  as  possible ;  these  are  gradually  in- 
creased until  finally,  the  tiles  being  in  position,  the  copper  oxide 
begins  to  appear  dark  red.  The  water  deposited  at  the  beginning 
of  the  heating,  in  the  forward  cool  end  of  the  tube,  is  now  removed 
with  filter  paper  wrapped  around  a  glass  rod.  When  no  more 
water  collects,  the  front  end  of  the  tube  is  closed  by  a  ru  ;>b^r 
stopper  bearing  the  straight  calcium  chloride  tube.  After  atnut 
20  or  30  minutes'  heating  the  burners  under  the  copper  oxide 
spiral,  the  adjacent  empty  space,  and  those  under  about  5  cm.  of 
the  copper  oxide  layer  lying  next,  are  extinguished,  and  at  the 
same  time  the  current  of  oxygen  is  cut  off. 

Weighing  the  Absorption  Apparatus  and  the  Substance.  —  While 
the  rear  part  of  the  tube  is  cooling,  the  calcium  chloride  tube,  the 
potash  bulbs,  and  the  substance  are  weighed.  Before  the  absor^ 
tion  apparatus  is  weighed,  it  is  wiped  off  with  a  clean  cloth,  free 
from  lint,  and  the  rubber  tubing  and  glass  rods  removed  ;  after  the 
weighing,  these  are  replaced.  The  substance,  if  solid,  is  weighed 
in  a  porcelain  boat  which  has  previously  been  heated  strongly,  and 
cooled  in  a  desiccator.  The  boat  is  first  weighed  empty,  0.15  to 
0.20  gramme  of  the  substance  placed  in  it  and  weighed  again ;  it 
is  then  placed  on  a  tin-foil-covered  cork,  in  which  a  suitable  groove 
has  been  cut,  and  transferred  to  a  desiccator. 

The  Combustion.  —  When  the  rear  end  of  the  tube  is  cold,  the 
copper  oxide  spiral  is  withdrawn  with  a  hooked  glass  rod  or  wire, 


S  cm.  free 

Short  copper  spiral 


45  cm.  coarse  oxide 


Short  copper  spiral 


10  cm.  free 


15  cm.  copper  oxide 
spiral 


5  cm.  free 

FIG.  60. 


I08  GENERAL  PART 

the  porcelain  boat  is  inserted  as  far  as  the  coarse  copper  oxide, 
care  being  taken  not  to  upset  the  boat,  and  finally  the  spiral  is 
replaced.  The  stop-cock  tube,  with  the  cork  closed,  is  then  put 
in  position.  The  straight  calcium  chloride  tube  is  replaced  by 
the  weighed  U-tube,  with  its  empty  bulb,  which  will  condense  the 
greater  portion  of  the  water,  nearest  the  furnace.  To  the  U-tube 
is  connected,  by  a  rubber  joint,  the  potash  apparatus,  and  the 
soda-lime  tube  of  the  latter  with  the  straight  calcium  chloride 
tube  in  the  same  way  (Fig.  61).  The  connecting  of  the  different 
parts  of  the  apparatus  may  be  facilitated  by  blowing  air  from  the 
lungs  through  each  rubber  joint  before  pushing  it  on  the  glass 
tubes.  Especial  care  is  taken  to  have  a  good  joint  between 
the  U -calcium  chloride  tube  and  the  potash  bulbs,  since  at  this 
point  very  commonly  lies  the  source  of  error  in  analyses  not  con- 
cordant. A  thick-walled  seamless  rubber  tubing  is  employed  ; 
it  is  drawn  over  the  two  ends  of  the  glass  tubes  until  they  touch. 
In  order  to  provide  against  any  possible  leak,  two  ligatures  of  thin 
copper  wire  or  "  wax  ends  "  are  bound  around  the  joints.  A  test 
as  to  whether  the  apparatus  is  perfectly  tight  is  not  always  con- 
vincing when  the  combustion  is  conducted  in  an  open  tube  ;  since, 
on  the  one  hand,  the  heating  is1  not  constant,  and  on  the  other, 
in  consequence  of  the  friction  of  the  solution  in  the  narrow  tubes, 
a  leak,  at  times,  may  not  be  detected.  '  The  rubber  stoppers 
closing  the  tube  may  be  protected  from  the  heat  by  placing  on 
the  tube,  close  to  the  furnace,  an  asbestos  plate  with  a  circular 
hole  in  the  centre.  After  closing  the  screw  pinch-cock,  the  glass- 
cock  is  opened,  and  a  slow  current  of  oxygen  (two  bubbles  per 
second)  is  admitted  to  the  tube  by  carefully  opening  the  pinch - 
cock.  Small  flames  are  now  lighted  under  the  copper  oxide 
spiral,  which  are  increased  after  some  time,  until,  finally,  the  spiral 
is  brought  to  a  dark  red  glow.  When  this  is  done,  the  flames 
under  the  unheated  copper  oxide  are  gradually  lighted,  care  being 
taken  not  to  allow  any  flame  near  the  porcelain  boat  to  be  too 
large.  Now  follows  the  most  difficult  operation  of  the  analysis, 
upon  which  the  success  of  it  virtually  depends,  viz.  the  gradual 
heating  of  the  substance.  This  is  conducted  in  exactly  the  same 


ORGANIC  ANALYTICAL   METHODS  1 09 

way  as  that  given  under  the  nitrogen  determination.  The  heating 
is  begun,  at  first,  with  a  single  small  flame ;  this  is  gradually  in- 
creased in  size,  or  several  others  may  be  lighted,  then  the  tube  is 
covered  on  one  side  with  the  tiles,  and  after  a  short  time,  on  the 
other,  and  finally  the  full  flames  are  used.  With  easily  volatile 
substances,  the  heating  at  the  beginning  is  not  done  with  the 
flame,  but  by  covering  that  portion  of  the  tube  containing  the 
boat  with  hot  tiles,  taken  from  the  forward  highly  heated  portion 
of  the  furnace.  Numerous  modifications  have  been  applied  to 
this  most  difficult  part  of  the  analysis,  concerning  which  no  satis- 
factory general  directions  can  be  given.  A  valuable  rule  is  to 
conduct  the  heating  in  such  a  way  that  the  gas  bubbles  passing 
through  the  potash  apparatus  follow  one  another  with  as  slow  a 
regularity  as  possible.  If  the  passage  of  bubbles  becomes  too 
rapid,  the  heating  is  moderated.  If,  during  the  combustion, 
water  should  condense  in  the  glass-cock,  or  in  the  rear,  cold 
portion  of  the  tube,  as  it  always  does  in  the  front  end,  it  is 
removed  by  holding  a  hot  tile  under  it,  or  by  heating  with  a  small 
flame.  When  the  boat  has  been  heated  some  time  with  the  full 
flames,  the  combustion  is  considered  to  be  ended.  In  order  to 
drive  the  last  portions  of  carbon  dioxide  and  water  from  the  tube 
into  the  absorption  apparatus,  a  somewhat  more  rapid  current  of 
oxygen  is  passed  through  the  tube,  until  a  glowing  splinter  held 
before  the  opening  of  the  straight  calcium  chloride  tube  is  ignited. 
During  this  operation,  the  water,  condensed  for  the  most  part  in 
the  front  end  of  the  tube,  is  also  driven  over  into  the  calcium 
chloride  tube,  as  above  described.  When  this  has  been  done,  the 
rubber  stopper  is  withdrawn  from  the  front  end  of  the  combustion 
tube,  care  being  taken  to  prevent  the  water  in  the  calcium  chloride 
tube  from  running  out.  To  remove  the  oxygen  in  the  absorption 
apparatus,  a  slow  current  of  air  which  need  not  be  dried  is  drawn 
through  it  for  1-2  minutes,  with  the  mouth  or  suction.  The 
apparatus  is  taken  apart,  closed  up  as  above  described,  allowed 
to  stand  in  the  weighing-room  for  half  an  hour,  and  is  then 
weighed.  From  the  difference  in  the  weights  of  the  absorption 
apparatus  before  and  after  the  combustion,  the  percentage  of 
carbon  and  hydrogen  is  found  from  the  following  equations  • 


HO  GENERAL   PART 

Wt.  CO2  X  300 

Percentage  of  Carbon      =— —  — , 

Wt.  Substance  x  n 

log  -£-=0.435 73-  i 

VyW2 

Wt.  H2O  X  201.6 
Percentage  of  Hydrogen  = 


Wt.  Substance  X  18.01 6' 

log -^-=0.04884 -i 
rl2U 

Modifications  of  the  Method.  —  In  many  cases  instead  of  using 
oxygen  for  the  ignition  of  the  copper  oxide,  the  same  result  may 
be  obtained  by  using  a  current  of  air.  The  combustion  may  also 
be  conducted  in  a  current  of  air ;  but  when  the  substance  is  diffi- 
cult to  burn,  it  is  still  necessary  toward  the  end  of  the  operation  to 
pass  oxygen  through  the  tube  for  some  time.  As  soon  as  a  glow- 
ing splinter  held  at  the  end  of  the  straight  calcium  chloride  tube 
is  ignited,  the  combustion  is  ended.  The  combustion  may  also  be 
conducted  without  passing  a  current  of  air  or  oxygen  into  the  tube 
at  the  beginning,  in  which  case  the  glass  stop-cock  is  closed. 
Under  these  conditions,  as  soon  as  the  substance  has  been 
heated  for  some  time  with  the  full  flames,  toward  the  end  of  the 
operation  the  glass  stop-cock  is  opened  and  a  current  of  air 
or  oxygen  passed  through  the  tube.  Substances  which  burn  with 
great  difficulty  can  also  be  mixed  with  fine  copper  oxide  in  a 
copper  boat  (see  below),  and  then  burned  in  the  same  way  in 
oxygen. 

Combustion  of  Substances  containing  Nitrogen.  —  Since  in  the 
combustion  of  nitrogenous  compounds,  the  reduced  copper  spiral 
serving  for  the  reduction  of  the  oxides  of  nitrogen  must  be  used, 
the  combustion  tube  is  charged  somewhat  differently  in  this  case. 
The  first  copper  roll  is  inserted  in  the  tube,  not  5  cm.,  but  15  cm., 
the  space  in  front  of  it  being  reserved  for  the  reduced  spiral. 
Consequently  the  layer  of  coarse  copper  oxide  is  but  35  cm.,  and 
not  45  cm.,  in  length.  No  change  is  made  in  the  disposition  of 
the  copper  oxide  spiral.  The  ignition  of  the  copper  oxide  is 
conducted  exactly  as  above,  except  that  a  current  of  air  is  used. 


ORGANIC  ANALYTICAL   METHODS  III 

If,  however,  the  ignition  should  be  conducted  throughout  with 
oxygen,  at  the  end  of  the  operation  this  is  displaced  by  air.  The 
further  operations  are  the  same  as  those  described  above,  except 
that  the  reduced  copper  spiral  is  put  in  position  last — just  before 
connecting  the  combustion  tube  with  the  absorption  apparatus. 
In  order  to  prevent  the  oxidation  of  the  copper,  the  combustion 
proper  is  performed  with  the  glass-cock  closed,  and  oxygen  is 
not  admitted  to  the  tube  until  at  the  end.  As  soon  as  the  oxy- 
gen is  admitted,  the  flames  under  the  reduced  copper  spiral  are 
extinguished.  The  gas  is  passed  through  until  it  can  be  detected 
at  the  end  of  the  apparatus  as  above  described.  In  the 
combustion  of  substances  which  leave  a  charred,  difficultly 
combustible,  nitrogenous  residue,  it  is  necessary  to  burn  them 
by  mixing  with  fine  copper  oxide.  Since  the  porcelain  boats 
are  generally  too  small  to  contain  a  sufficient  quantity  of  this, 
a  boat  made  of  sheet  copper,  8  cm.  long  and  of  a  width  suffi- 
cient to  enable  it  to  be  just  passed  into  the  tube,  is  used.  It 
is  filled  as  follows :  After  it  has  been  previously  ignited,  it  is 
placed  upon  a  sheet  of  black  glazed  paper,  and  half  filled  with 
fine  copper  oxide  also  previously  ignited  and  afterwards  cooled 
in  a  desiccator.  Upon  this  is  carefully  spread  the  weighed  sub- 
stance from  a  weighing-tube  as  in  the  nitrogen  determination, 
then  a  layer  of  fine  copper  oxide  is  added  until  the  boat  is 
three-fourths  full :  the  substances  are  now  well  mixed  by  care- 
ful stirring  with  a  thick  platinum  wire.  If  some  of  the  mixture 
should  fall  upon  the  glazed  paper,  it  is  returned  to  the  boat  with 
the  aid  of  a  feather  or  brush.  The  combustion  is  made  with  the 
glass-cock  closed.  Oxygen  is  not  admitted  until  at  the  end  of 
the  operation. 

Combustion  of  Substances  containing  Sulphur  or  a  Halogen.— 
Sulphur  compounds  cannot  be  burned  with  copper  oxide  in 
the  manner  described,  since  at  a  red  heat  the  copper  sulphate 
formed  gives  off  sulphurous  acid,  which  is  absorbed  by  the 
potash  apparatus  along  with  the  carbon  dioxide,  giving  a  result 
in  which  the  percentage  of  carbon  is  too  high.  In  this  case 
the  oxidation  is  accomplished  with  granulated  lead  chromate. 


H2  GENERAL   PART 

The  filling  of  the  tube,  open  at  both  ends,  is  done  just  as  described 
above :  copper  oxide  spiral,  empty  space  for  boat,  long  layer  of 
lead  chromate.  The  ignition  in  oxygen,  etc.,  is  also  the  same. 
But  two  points  are  here  to  be  observed :  (i)  the  lead  chro- 
mate is  not  heated  as  strongly  as  the  copper  oxide,  otherwise 
it  fuses  in  the  glass;  and  (2)  the  most  forward  portion  of 
the  lead  chromate  layer,  nearest  the  calcium  chloride  tube 
(that  above  about  three  burners),  is  heated  very  slightly,  since 
lead  sulphate  is  not  completely  stable  at  a  red  heat.  The  sub- 
stance is  mixed  in  the  copper  boat  with  powdered,  ignited  lead 
chromate. 

Halogen  compounds  can  be  burned  in  the  usual  way  with  cop- 
per oxide ;  but  since  the  copper  halides  are  partially  volatile  and 
give  up  the  halogen  on  being  heated  to  redness,  a  silver  spiral 
must  be  inserted  in  the  tube  to  retain  the  halogen.  The  tube  is 
filled  in  the  same  way  as  for  the  combustion  of  a  nitrogen  com- 
pound, only  in  place  of  the  reduced  copper  spiral,  one  of  silver 
is  used.  But  it  is  better  to  perform  the  combustion  with  lead 
chromate,  in  which  case  it  will  not  be  necessary  to  use  a  silver 
spiral.  Since  the  lead  halides  are  also  somewhat  volatile  at  a  red 
heat,  so,  as  above,  the  front  part  of  the  tube  containing  the  lead 
chromate  is  heated  but  slightly. 

Combustion  of  Liquids.  —  If  the  compound  to  be  analysed  is  a 
liquid,  it  can  be  weighed  directly  in  the  porcelain  boat,  provided 
it  is  very  difficultly  volatile.  Moderately  volatile  substances 
are  weighed  in  a  small  glass  tube  which  is  loosely  closed 
with  a  glass  stopper  (see  Fig.  53,  page  81).  In  order  to 
introduce  this  into  the  tube,  it  is  placed  in  the  porcelain 
boat  in  such  a  position  that  the  mouth  of  the  tube  is 
directed  upwards.  A  preliminary  trial  will  show  whether 
the  boat  containing  the  empty  tube  will  pass  into  the  com- 
bustion tube.  Very  easily  volatile  substances  are  weighed 
2'  in  small  bulb-tubes  which  are  sealed  after  weighing  (Fig. 
62).  The  filling  is  done  as  follows  :  The  empty  tube  is  weighed, 
heated  gently,  and  the  open  end  dipped  under  the  liquid  to  be 
analysed.  On  cooling,  the  liquid  will  be  drawn  up  into  the  bulb. 


ORGANIC  ANALYTICAL   METHODS  113 

If  a  sufficient  quantity  is  not  obtained  the  first  time,  the  operation 
is  repeated ;  before  it  is  sealed  care  must  be  taken  that  the 
capillary  contains  none  of  the  liquid ;  if  it  does,  it  must  be 
removed  by  heating.  It  is  now  sealed,  and  the  tube  plus  sub- 
stance weighed.  Care  must  again  be  taken  to  prevent  any  of  the 
liquid  from  finding  its  way  into  the  'capillary,  due  to  sudden 
movements  or  other  causes.  To  prepare  the  tube  for  the  com- 
bustion, the  extreme  end  is  filed  and  broken  off,  during  which 
operation  the  tube  is  not  held  by  the  bulb.  It  is  placed  in  the 
boat  with  its  open  end  elevated  'and  directed  toward  the  front 
end  of  the  furnace.  The  precaution  to  ascertain  beforehand 
whether  the  boat  loaded  with  the  tube  will  pass  into  the  com- 
bustion tube,  should  always  be  taken.  If  necessary,  the  capillary 
is  shortened. 


ELEMENTARY  ANALYSIS 
DENNSTEDT'S  METHOD 

Dennstedt's  method  consists  in  burning  the  substance  with  free 
oxygen  x  exclusively,  in  the  presence  of  platinum  as  contact  sub- 
stance (catalyser). 

In  addition  to  the  frame  of  a  combustion  furnace,  and  an  oxy- 
gen gasometer, —  Dennstedt  recommends  the  use  of  two  flasks 
provided  with  tubulures  at  the  bottom  and  having  a  capacity  of  5 
litres,  —  the  requisites  for  analysis  are  : 

1.  A  hard  glass  tube  open  at  both  ends ;  length  86  cm. ;  diame- 
ter 18-20  mm.  ;  also  an  inner  tube  and  a  small  wash  bottle. 

2.  A  drying  tower  for  the  oxygen. 

3.  A  U-shaped  calcium  chloride  tube  with  two  ground  stop- 
cocks and  a  ground-in  stopper  (next  to  the  bulb). 

4.  A  soda-lime  tower  with  two  ground  stoppers. 

5.  A    U-shaped   soda-lime-calcium    chloride    tube    with    two 
ground  stop-cocks  ("Testing-tube  "). 


1  Not  electrolytically  prepared. 
I 


114 


GENERAL   PART 


6.  A  wash  bottle  for  palladious  chloride  ("  Palladium  bottle  ") 

7.  A  straight  calcium  chloride  tube. 

8.  A  strip  of  star-shaped  platinum,  and  a  roll  of  thin  platinum 
foil. 

9.  A  rod  of  hard  glass  for  the  inner  tube,  with  a  loop  and  plati- 
num thread  or  platinum  wire. 

10.  A  porcelain   boat  (for  the  substance)  divided  into  three 
parts,  length  8  cm.  ;  also  several  ordinary  porcelain  boats  (Absorp- 
tion boats). 

11.  Rubber  stoppers  and  seamless  rubber  tubing,  to  be  used 
for  the  analysis  only. 

12.  Chemicals:    calcium  chloride,  soda-lime,  palladious  chlo 
ride,  lead  peroxide,  minium,  sodium  carbonate,  molecular  silver. 

1.  The  Combustion  Furnace  consists  of  two  stands  supporting 
three  loose  iron  troughs.  The  middle  one  is  covered  with  thin 
asbestos  paper,  and  serves  as  a  support  for  the  combustion  tube, 
while  the  other  two  troughs  support  the  covers,  the  inner  surfaces 
of  which  are  lined  with  asbestos.  Of  these  five  are  needed  ;  a 
large  cover  25  cm.  in  length,  and  four  smaller  covers  each  one 
having  a  length  of  12  cm.  Of  the  latter,  one  is  provided  with  a 


FIG.  62  A. 

sliding  window  of  mica  (10  cm.  :  2  cm.),  through  which  the  cata- 
lyser  may  be  observed.  The  sheet  of  mica  is  renewed  when  it 
becomes  opaque.  The  iron  covers  are  provided  with  projections 
on  the  upper  edges,  and  may  be  moved  back  and  forth  with  crucible 
tongs.  They  should  not  touch  the  combustion  tube.  The  com- 
bustion tube  is  heated  with  three,  or  preferably  four,  burners.  The 


ORGANIC  ANALYTICAL   METHODS  115 

two  burners  shown  at  the  left  of  Fig.  62  A  are  used  to  vaporise 
the  substance.  They  are  Bunsen  orTeclue  burners  to  which  wing 
burners  may  be  attached.  One  burner  is  sometimes  used  for  the 
purpose.  Then  follows  a  stronger  Bunsen  or  Teclue  burner,  pro- 
vided with  a  wing  burner  and  a  regulation  device.  This  is  placed 
under  the  contact  star  and  supplies  the  combustion  flame.  The 
rear  of  the  tube  (the  part  preceding  the  absorption  apparatus)  is 
heated  with  a  movable  flame  tube  consisting  of  20  non-luminous 
flames.  During  the  combustion  a  temperature  of  300-320°  is 
necessary  in  this  part  of  the  tube.  The  height  of  the  flames  that 
will  produce  this  temperature  is  determined  in  a  preliminary  ex- 
periment by  inserting  a  thermometer  in  the  combustion  tube. 

2.  Drying  Tower  for  the  Oxygen.  —  Pure  concentrated  sulphuric 
acid  is  poured  into  the  lower  part  of  the  tower  (Fig  62  A,  left)  to  a 
height  of  2  cm.,  so  that  the  end  of  the  conducting  tube,  which  is 
2   mm.  wide,  dips  into   this  to   a  depth  of  J-i   cm.     Ligatures 
(string  or   wire)   are  bound  around  the  joints.     A  small  funnel, 
with  its  tube  bent  sidewise,  is  introduced  into  the  lower  narrow 
part  of  the  tower.     The  funnel  is  covered  with  a  little  glass-wool 
or  cotton,  and  the  lower  half  of  the  cylindrical  tower  (about  10 
cm.)  is  filled  with  coarse,  sifted  soda-lime ;  the  upper  half  is  filled 
with  calcium  chloride.     Then  follows  a  layer  of  glass-wool  or  cot- 
ton.    Concerning  the  quality  of  the  soda-lime  and  the  calcium 
chloride,  see  below  (Filling  of  absorption  apparatus). 

3.  The  Small  Wash  Bottle.  —  A  plug  of  cotton  is  placed  at  the 
bottom  of  the  wide  tube  attached  to  the  small  wash  bottle  (Fig. 
62  B)  ;  it  is  then  filled  with  calcium  chloride  and  covered  with  a 
layer  of  cotton  (see  4  a).     The  lower  narrow  part  of  the  small 
wash  bottle  is  filled  with  concentrated  sulphuric  acid.     A  capillary 
tube  is  used  for  this  purpose.     The  bottle  is  held  in  an  inverted 
position  ;  the  tip  of  the  capillary  is  now  inserted  as  far  into  the 
U-shaped  curve  as  possible,  and  by  proper  manipulation  the  acid 
is  allowed  to  flow  through  the  inner  bulb  into  the  lower  narrow 
end.     The  limb  nearest  the  calcium  chloride  tube  is  dried  with 
blotting-paper.     The  small  wash  bottle  must  be   constructed  so 
that  there  is  a  space  of  at  least  i  mm.  between  the  inner  bulb  and 


GENERAL   PART 


the  outer  tube.  The  connecting  parts  of  the  apparatus  may  be 
made  tight  by  moistening  the  two  holes  of  the  stopper,  as  well  as 
its  lower  surface,  with  a  saturated  solution  of  calcium  chloride. 
In  order  to  regulate  the  stream  of  oxygen  as  perfectly  as  possible 
by  the  aid  of  the  three  stop-cocks  of  the  small  wash  bottle,  the 
perforations  of  the  cocks  are  filed  on  both  sides  with  a  sharp  tri- 
angular file,  as  seen  in  Fig.  620.  The  calcium  chloride  is  renewed 
from  time  to  time,  and  the  stoppers  are  kept  closed  when  the 
apparatus  is  not  in  use. 

4.    Absorption    Apparatus.  —  (a)   Calcium    Chloride    Tube.     It 
contains  two  ground  stop-cocks,  a  small  ground  glass   stopper, 


FIG.  62  B. 


FIG.  62  c. 


and  the  bulb  in  which  a  greater  part  of  the  water  condenses.  The 
previously  sifted  calcium  chloride  is  poured  into  a  wide  test-tube, 
clamped  in  a  slanting  position,  and  carefully  heated  with  a  free 
flame  until  no  more  water  deposits  in  the  cooler  part  of  the  tube. 
The  heating  must  be  done  cautiously,  and  only  for  a  short  time. 
In  filling  the  U-tube  care  must  be  taken  that  no  dust  particles  or 
calcium  chloride  settle  in  the  side-tubes ;  to  prevent  this  the  side- 


ORGANIC   ANALYTICAL   METHODS  II 7 

tubes  are  plugged  with  cotton  during  the  filling.  The  cotton  is 
removed  with  forceps  after  filling  the  tube.  A  short  roll  of  paper 
may  also  serve  the  same  purpose,  protecting  not  only  the  side-tubes 
but  also  the  ground  part  of  the  U-tube.  A  roll  of  cotton  is  finally 
introduced  into  the  calcium  chloride  tube.  The  ground  parts  of 
the  tube  are  then  cleaned  and  slightly  oiled.  Before  the  newly 
filled  tube  is  used,  dry  carbon  dioxide  is  passed  through  it  (see 
page  103).  The  carbon  dioxide  is  then  displaced  by  oxygen. 

(b)  Soda-lime  Tower.     Commercial  soda-lime  is  often  too  dry 
and  does  not  therefore  readily  absorb  carbon  dioxide.     Before 
filling  the  absorption  apparatus  a  few  grammes  are  carefully  heated 
in  a  test-tube  over  a  free  flame.     Much  water  should  condense  in 
the  cooler  parts  of  the  tube.     If  this  is  not  the  case,  the  entire 
quantity  is  moistened  with  the  necessary  amount  of  water  (spray). 
The  soda-lime  must  be  freed  from  small  particles  by  sifting,  and 
care  must  be  taken  that  no  small  particles  settle  in  the  side-tubes. 
The  precautions  outlined  for  calcium  chloride  are  followed  here. 
As  soda-lime  expands  by  the  absorption  of  carbon  dioxide,  in  order 
to  avoid  the  danger  of  breaking  the  apparatus  care  is  taken  not  to 
use  too  much.     The  perforations  of  the  glass  stoppers  are  then 
filled  with   dry  cotton ;    the   ground  surfaces  are  very  carefully 
cleaned,  and  slightly  greased.     When  it  is  desired  to  refill  a  tower 
that  has  been  used,  the  stoppers  are  removed,  the  apparatus  is 
freed  from  grease,  and  dipped  for  several  hours  in  water  that  has 
been  slightly  acidified  with  hydrochloric  acid.     During  the  com- 
bustion the  tower  is  always  kept  in  the  same  position ;  in  order  to 
prevent  mistakes  the  side-tubes  are  marked  (arrow,  or  coloured 
glass-button).- 

(c)  Soda-lime-calcium   Chloride  Tube  ("Testing- Tube").     One 
limb  of  this  tube  is  filled  with  soda-lime  and  the  other  with  calcium 
chloride.    The  precautions  mentioned  in  (a]  and  (<£)  are  observed. 
The  testing-tube  is  inserted  in  such  a  manner  that  the  soda-lime 
limb  is  next  to  the  soda-lime  tower. 

(d)  The    Weighing  of  the  Absorption  Apparatus.     The   three 
absorption  tubes  are  always  filled  with  oxygen  before  weighing. 
When  used  for  the  first  time,  dry  oxygen  is  conducted  into  the 


H8  GENERAL   PART 

apparatus  until  all  the  air  has  been  driven  out.  (Test :  vigorous 
flaming  of  a  glowing  splinter.)  One  of  the  two  stop-cocks  in  each 
apparatus  is  opened  for  a  moment  before  weighing,  in  order  to 
equalise  the  differences  in  pressure.  In  weighing  after  a  combus- 
tion, the  temperature  should  be  as  nearly  the  same  as  it  was  before 
combustion.  In  most  cases  it  is  sufficient  to  carry  out  the  final 
weighing  when  the  apparatus  has  remained  in  the  balance  room 
for  one  or  two  hours.  It  is  safer  to  check  the  weighing  on  the 
following  morning.  In  winter-time  the  temperature  of  the  balance 
room  should  be  kept  uniform  over  night.  Should  a  long  period 
elapse  between  two  analyses,  the  apparatus  is  again  filled  with 
oxygen. 

(e)  The  Palladious  Chloride  Wash  Bottle  (" Palladium  Bottle") 
is  half  filled  with  a  clear  dilute  water  solution  of  palladious  chloride 
of  a  straw-yellow  colour.  The  solution  is  filtered  when  it  becomes 
cloudy.  The  separation  of  palladium  (by  the  action  of  carbon 
monoxide)  indicates  an  incomplete  combustion.  In  addition  to 
this  the  solution  is  also  of  service  in  showing  the  rate  of  flow  of 
the  gas  stream. 

5.  The  Combustion  Tube  and  Accessories.  —  All  combustions 
are  carried  out  by  the  use  of  a  duplex  supply  of  oxygen.  For  this 
purpose  a  T-tube  is  inserted  in  the  stopper  in  the  rear  end  of  the 
combustion  tube.  The  vertical  limb  of  the  T-tube  is  provided  with 
a  stop-cock,  and  is  connected  with  the  calcium  chloride  tube  of 
the  small  wash  bottle  as  shown  in  Fig.  62  B.  Through  the  hori- 
zontal part  of  the  T-tube  passes  the  capillary  of  the  inner  tube ; 
these  two  are  connected  with  a  short  rubber  tubing  (ligature). 
The  wider  part  of  the  inner  tube  fills  the  space  inside  the  com- 
bustion tube  almost  completely,  and  serves  as  a  receiver  for  the 
boat  containing  the  substance  taken  for  analysis.  In  order  to 
prevent  the  fusion  of  the  inner  tube  into  the  combustion  tube,  a 
coil  of  fairly  thick  platinum  wire  is  placed  around  the  wide,  open 
end  of  the  former.  Furthermore,  in  order  to  prevent  the  forma- 
tion of  an  explosive  mixture  by  the  combustible  vapours  and  the 
oxygen,  a  rod  of  hard  glass  is  introduced  into  the  inner  tube. 
The  rod  is  .of  a  size  that  nearly  fills  the  empty  space  in  the  inner 


ORGANIC  ANALYTICAL   METHODS  1 19 

tube.  It  is  provided  with  a  loop  in  the  fore-part ;  to  this  is 
attached  a  roll  of  platinum  wire  which  reaches  the  open  end  of 
the  inner  tube.  Or,  instead  of  the  platinum  roll,  a  thin  platinum 
wire  is  wound  around  the  rod.  This  arrangement  will  also  prevent 
the  rod  from  fusing.  The  glass  rod  is  unnecessary  in  most  in- 
stances. Its  place  is  taken  by  a  roll  of  thin  platinum  foil.  This  is 
placed  at  the  opening  of  the  inner  tube  in  such  a  way  that  one 
half  rests  in  the  inner  tube,  the  other  half  in  the  combustion  tube  ; 
then  follows  the  contact  star.  Vapours  of  high  boiling  substances 
will  sometimes  condense  and  run  into  the  inner  tube.  In  order 
to  protect  the  tube,  it  is  covered  to  within  i  cm.  of  the  opening 
and  over  one-third  of  the  inner  surface  with  a  strip  of  thin  asbestos 
paper.  This  must  be  heated  with  the  combustion  tube  in  a  stream 
of  oxygen  during  the  drying  of  the  apparatus.  (In  the  simulta- 
neous estimation  of  sulphur  the  asbestos  is  not  used.)  Before  the 
analysis,  the  previously  washed  and  dried  combustion  tube,  the 
inner  tube  (including  the  glass  rod),  the  platinum  coil,  and  the 
platinum  star  are  heated  for  a  while  in  a  moderate  stream  of 
oxygen  at  250-300°.  During  the  heating  the  burners  are  evenly 
distributed,  and  the  covers  are  placed  in  position.  The  opening 
at  the  forward  end  is  finally  closed  with  a  straight  calcium  chloride 
tube,  and  the  combustion  tube  is  allowed  to  cool  in  a  stream  of 
oxygen.  As  the  bulky  Dennstedt  tubes  break  more  readily  than 
those  used  in  Liebig's  method,  special  care  is  exercised  in  the 
heating  as  well  as  the  cooling  of  the  former,  and  in  exposing  them 
to  sudden  changes  of  temperature.  It  is  also  necessary,  at  all 
times,  to  prevent  the  covers  from  coming  in  contact  with  the 
hot  tube. 

6.  The  Combustion  Proper.  —  In  combustions  by  Liebig's  method 
it  has  not  been  found  possible  to  prescribe  details  that  will  cover 
all  cases.  This  is  still  less  possible  in  Dennstedt's  method,  in 
which  the  number  of  modifications  and  combinations  is  much 
greater.  A  general  outline  of  the  method  will  be  given  for  sub- 
stances containing  carbon,  hydrogen  and  oxygen,  and  Dennstedt's 
own  words  will  be  used  in 'part. 

While  the  combustion  tube  is  being  heated  and  cooled  in  a 


120  GENERAL   PART 

stream  of  oxygen,  the  absorption  apparatus  is  weighed  (a  stop-cock 
is  opened  for  an  instant)  ;  the  boat  having  the  three  divisions  is 
also  weighed,  first  empty,  and  then  with  the  substance.  The 
supply  of  oxygen  is  now  cut  off,  and  the  inner  tube  (with  small 
wash  bottle,  etc.)  is  withdrawn  by  removing  the  stopper  at  the  rear 
end  of  the  combustion  tube.  The  long  rubber  connection  be- 
tween the  drying  tower  and  the  small  wash  bottle  is  not  removed. 
The  boat  containing  the  substance  is  introduced  into  the  inner 
tube,  and  pushed  in,  as  far  as  possible.  Then  follows  the  glass 
rod  with  its  platinum  wire,  or  the  platinum  roll  alone,  as  described 
above,  and  the  apparatus  is  securely  attached  to  the  combustion 
tube.  The  different  parts  of  the  absorption  apparatus  are  finally 
connected  by  the  use  of  short,  thick-walled,  seamless  rubber  joints. 
The  rubber  should  be  drawn  over  the  ends  of  the  glass  tubes  until 
they  touch.  The  Hrnb  of  the  U-tube  containing  soda-lime 
should  be  kept  next  to  the  soda-lime  tower.  The  drying  apparatus 
is  most  conveniently  connected  with  the  combustion  tube  in  the 
following  manner  :  A  rubber  stopper  is  first  placed  on  the  calcium 
chloride  tube  (at  the  bulb  end) ;  the  tube  is  then  connected  with 
the  soda-lime  tower,  which  is  in  turn  attached  to  the  testing-tube ; 
and  finally,  the  end  of  the  combustion  tube  is  securely  closed  by 
the  rubber  bearing  the  calcium  chloride  tube.  Then  follows  the 
palladium  bottle. 

Before  the  combustion  proper,  a  test  as  to  whether  the  apparatus 
is  perfectly  tight  is  conducted  in  the  following  manner :  All  the 
stop-cocks,  from  the  stopper  of  the  gasometer  to  the  last  stopper 
of  the  U-tube  (testing- tube)  are  closed.  The  stop-cock  of  the 
gasometer  and  the  lower  stop-cock  of  the  drying  tower  are  now 
opened,  so  that  a  few  gas  bubbles  pass  through  the  sulphuric  acid. 
If  the  joints  are  perfectly  tight,  the  bubbling  will  stop  as  soon  as 
the  pressure  between  gasometer  and  drying  tower  ,is  equalised.  If 
the  bubbling  continues,  then  there  is  a  leak  which  must  be  pre- 
vented. The  upper  stop-cock  of  the  drying  tower  is  now  opened, 
and  left  open  until  the  bubbling  stops.-  This  is  continued  to 
the  last  stop-cock  of  the  testing- tube.  During  this  test,  the  stop- 
cock of  the  small  wash  bottle  containing  sulphuric  acid  is  opened 


ORGANIC  ANALYTICAL   METHODS  12 1 

in  such  a  way  that  not  more  than  two  bubbles  per  second  escape. 
The  combustion  is  commenced  when  the  apparatus  is  found  to  be 
perfectly  tight.  "  For  its  success  it  is  absolutely  necessary  to 
thoroughly  mix  the  vapour  of  the  burning  compound  when  it 
reaches  .the  contact  substance  (platinum)  with  as  much  oxygen  at 
every  instant  as  is  required  for  its  complete  combustion,  i.e.  there 
should  always  be  present  an  excess  of  oxygen.  In  the  combustion 
of  volatile  substances,  in  order  to  mix  the  vapour  with  the  proper 
quantity  of  oxygen,  the  oxygen  stream  is  introduced  in  two  parts ; 
one  part  is  known  as  the  slow  vaporising  stream,  which  sweeps 
over  the  burning  substance,  and  carries  away  its  vapour  in  a 
regular  manner ;  the  other  part  is  known  as  the  combustion  stream, 
which  meets  the  vaporising  stream  near  the  glowing  platinum." 
The  former  is  regulated  through  the  stop-cock  of  the  small  wash 
bottle  (Fig.  62  B,  upper  left  hand),  the  latter  through  the  stop-cock 
of  the  calcium  chloride  tube  (Fig.  62  B,  upper  right  hand).  The 
lower  stop-cock  of  the  calcium  chloride  tube  permits  the  passage 
of  both  streams.  The  small  wash  bottle  shows  the  velocity  of  the 
vaporising  stream,  and  the  palladium  bottle  that  of  the  combus- 
tion stream.  Whenever  the  velocity  of  these  streams  is  specified, 
e.g.  by  the  number  of  bubbles  for  every  10  seconds,  it  is  under- 
stood that  the  bubbles  in  the  small  wash  bottle  are  much  smaller 
than  those  in  the  palladium  bottle.  The  outer  stream  is  regulated 
in  such  a  manner  that  in  10  seconds  10-15  bubbles  pass  through 
the  palladium  bottle.  "  When  the  vaporisation  of  the  substance 
becomes  too  rapid,  the  velocity  of  this  stream  may  be  temporarily 
doubled,  or  increased  even  more,  without  hesitation."  The  inner 
stream  is  so  regulated  that  if  the  substance  is  easily  volatile,  5-10 
bubbles  pass  through  the  small  wash  bottle  every  10  seconds,  and 
if  the  substance  is  not  easily  volatile  10-30  bubbles  pass  through 
the  wash  bottle  every  10  seconds.  The  velocity  of  the  inner  stream 
should  not  be  altered  in  the  early  part  of  the  combustion.  A  small 
flame  is  first  lighted  under  the  contact  star.  This  is  gradually  in- 
creased, until  finally  the  star  appears  to  glow  brightly  through  the 
mica  window  of  the  small  cover.  The  flame,  the  small  cover,  and 
the  end  of  the  inner  tube  lie  in  the  same  vertical  plane.  The 


122  GENERAL   PART 

forward  empty  part  of  the  combustion  tube  is  heated  at  the  sarnt 
time  to  about  300°  with  the  burner  tube,  and  a  large  cover  is 
placed  next  to  the  small  cover  with  the  mica  window.  "The 
burner  used  to  vaporise  the  substance  is  turned  on  almost  entirely, 
and  burns  with  a  moderately  high  flame.  It  is  now  placed  at  the 
rear  and  kept  so  far  away  from  the  boats  that  even  very  volatile 
substances  are  just  vaporised  without  undergoing  much  change. 
When  the  contact  substance  begins  to  glow  brightly,  the  vaporis- 
ing flame  is  quickly  moved  forward,  about  i  cm.  every  3-4  minutes, 
depending  upon  the  volatility  of  the  substance,  until  the  latter 
melts  or  begins  to  decompose.  With  substances  that  do  not 
vaporise  or  decompose  readily,  the  flame  is  brought  near  the  boat. 
It  is  then  allowed  to  remain  undisturbed.  An  observation  will 
now  show  whether  the  contact  substance  is  glowing,  whether  there 
is  condensation  of  water  at  the  forward  end  of  the  tube,  in  short, 
whether  combustion  proper  has  started.  If  this  is  the  case,  every- 
thing is  left  unchanged  for  15  minutes.  If  combustion  does  not 
progress  smoothly  at  the  end  of  this  period,  the  combustion  flame 
and  the  cover  are  moved  1-2  mm.  to  the  rear.  This  is  repeated 
after  a  short  time,  until  it  is  found  that,  depending  upon  the  nature 
of  the  substance,  it  begins  to  burn  completely,  i.e.  it  first  melts, 
and  then  chars,  etc.,  even  in  the  first  division  of  the  boat.  Should 
the  decomposition  slow  down,  the  combustion  flame  and  the  cover 
are  slowly,  millimetre  by  millimetre,  moved  backwards,  until  finally 
there  is  complete  vaporisation,  decomposition,  or  charring.  The 
combustion  flame  should  never  be  moved  far  enough  to  diminish  the 
glow  of  the  platinum  at  the  open  end  of  the  inner  tube.  The  cover, 
however,  may  be  moved  back  and  kept  directly  above  the  boat. 
The  position  of  the  burners  need  not  be  changed  when  the  contact 
mass  is  seen  to  glow  brightly,  since  this  is  only  an  indication  that 
the  combustion  is  progressing  briskly.  But  if  the  glowing  is  very 
sudden  and  too  active,  or,  if  flames  appear  at  the  open  end  of  the 
inner  tube,  both  burners  are  pushed  backwards  in  order  to  prevent 
rapid  decomposition,  and  the  vaporising  flame  is  again  brought 
near  the  boat  in  order  to  secure  normal  conditions  once  more. 
The  combustion  flame  is  also  moved  back  gradually  to  the  extreme 


ORGANIC  ANALYTICAL   METHODS  123 

limit.  Should  this  stop  the  progress  of  the  combustion,  the  va- 
porising flame  is  moved  forward,  and  the  cover  at  the  rear  of  the 
tube  is  put  in  position.  When  the  contents  of  the  boat  have  either 
entirely  disappeared,  or  are  completely  carbonised,  the  inner 
stream  of  oxygen  is  increased,  and  the  tube  heated  to  redness." 
The  part  of  the  tube  adjacent  to  the  absorption  apparatus  is  finally 
covered  with  a  small  cover. 

When  the  combustion  is  ended,  the  flames  are  first  lowered  and 
then  turned  off  entirely,  and  the  apparatus  is  cooled  in  a  stream 
of  oxygen.  The  palladium  bottle  is  now  removed.  The  lower 
stop- cock  of  the  drying  tower  is  first  closed,  and  the  absorption  ap- 
paratus is  taken  apart  after  turning  off  the  stop-cocks.  The  small 
stopper  near  the  bulb  of  the  calcium  chloride  tube  must  not  be 
forgotten.  Concerning  the  weighing  of  the  apparatus  see  direc- 
tions given  above.  Under  normal  conditions,  the  soda-lime- 
calcium  chloride  tube  should  not  increase  in  weight  more  than  a 
few  milligrammes.  An  increase  in  weight  amounting  to  more 
than  10  mg.  indicates  that  the  soda-lime  tower  is  exhausted  and 
needs  refilling.  In  this  case  its  original  position  should  not  be 
reversed  by  oversight. 

Very  often  in  dealing  with  substances  that  are  not  very  volatile, 
it  is  more  convenient  to  use  two  vaporising  flames  in  place  of 
one.  Even  in  this  case  the  combustion  flame  under  the  platinum 
star  is  first  lighted.  The  flame  is  not  placed  under  the  substance, 
but  is  allowed  to  remain  under  the  contact  star.  The  vaporising 
flame  at  the  rear  is  also  kept,  as  before,  as  far  away  from  the  boat 
as  possible  ;  its  position  is  changed  only  towards  the  end  of  the 
combustion.  •  In  this  case  the  substance  is  vaporised  by  the  for- 
ward vaporising  flame,  which  is  kept  very  low  at  first  and  placed 
near  the  combustion  flame,  and  is  slowly  brought  near  the  boat 
with  a  gradual  increase  of  the  flame,  the  time  required  for  this 
being  the  same  as  that  given  above  for  the  combustion  flame.  As 
soon  as  the  forward  flame  is  brought  under  the  boat,  the  rear 
flame  is  also  pushed  towards  the  substance. 

It  is  to  be  noted  once  more  that  the  rate  of  the  combustion 
depends  upon  the  number  and  the  height  of  flames,  the  use  of 


I24  GENERAL   PART 

burners  without  or  with  wing  burners,  their  distance  from  the 
boat,  the  use  of  covers,  the  velocity  of  the  oxygen  stream,  etc. 
These  are  conditions  that  may  be  readily  controlled. 

Should  the  palladious  chloride  become  very  black  during  the 
combustion,  the  analysis  may  be  considered  unsuccessful.  Under 
these  conditions  either  the  absorption  apparatus  is  removed,  and 
the  tube  is  heated  to  glowing  in  the  presence  of  a  stream  of 
oxygen,  as  described  above  (the  absorption  apparatus  being  re- 
filled with  oxygen  for  a  new  analysis),  or  the  combustion  is 
brought  to  completion  as  under  normal  conditions.  The  weight 
of  the  absorption  apparatus  is,  of  course,  worthless  in  this  case. 
A  combustion  is  also  considered  unsuccessful  when  the  substance 
or  its  decomposition  products  sublime,  or  distil  beyond  the  con- 
tact star.  If  this  is  the  case,  the  absorption  apparatus  is  im- 
mediately removed,  and  the  tube  is  heated  to  glowing  in  the 
presence  of  a  stream  of  oxygen.  If  necessary,  the  absorption 
apparatus  is  freshly  prepared.  Finally,  weak  or  strong  explosions 
may  occur  inside  the  tube  during  the  combustion.  If  these  do 
not  produce  a  sublimate,  or  a  distillate,  and  cause  no  blackening 
of  the  palladious  chloride  solution,  then  the  analysis,  including  the 
final  weighing,  is  brought  to  a  normal  end.  If  analyses  give  per- 
sistently inaccurate  results,  a  blank  combustion  is  carried  on 
(without  substance)  to  ascertain  the  defect  in  the  apparatus. 

The  Combustion  of  Substances  containing  Nitrogen  or  Sulphur, 
or  both  at  the  same  time,  is  in  principle  exactly  the  same  as 
described  above,  with  the  only  modification  that,  in  order  to 
absorb  the  nitric  oxide,  the  sulphurous  acid,  and  sulphuric  acid,  a 
mixture  of  minium  and  lead  peroxide  is  placed  in  the  combustion 
tube  and  heated  to  320-350°  with  the  flame-tube. 

The  quality  of  lead  peroxide.  Lead  peroxide  especially  pre- 
prepared  for  the  Dennstedt  analysis  is  placed  on  the  market  by 
the  firms  of  Merck  and  Kahlbaum  under  the  label' of  "Lead 
Peroxide  according  to  Dennstedt."  But  Dennstedt's  investiga- 
tions show  that  even  these  pure  preparations  almost  always  contain 
small  quantities  of  organic  substances,  such  as  fibres,  dust  particles, 
etc.,  which  must  be  destroyed  before  the  substance  is  used.  This 


ORGANIC  ANALYTICAL   METHODS  125 

is  done  by  drying  a  large  quantity  on  a  watch  crystal  in  an  oven, 
at  a  temperature  of  120-140°,  and  heating  this  for  at  least  half  an 
hour,  or  longer,  in  a  hard  glass  tube  in  a  stream  of  oxygen  at 
320-350°.  For  the  preparation  of  minium  the  required  amount 
of  pure  lead  peroxide  is  heated  in  a  stream  of  air  at  400-450°, 
or  in  an  open  porcelain  dish,  until  the  dark-brown  colour  is 
changed  to  a  dull  red ;  it  is  then  allowed  to  cool  in  a  desiccator. 
Equal  quantities  of  lead  peroxide  and  minium  are  intimately 
mixed  and  used  for  the  analysis.  The  quantity  used  for  each 
analysis  is  7-8  grammes  (not  over  10  grammes)  of  the  mixture, 
weighed  out  to  within  -i-  gramme,  by  the  use  of  ordinary  weights. 
The  substance  is  introduced  into  the  tube  in  three  small  boats, 
the  boat  in  the  rear  containing  the  main  portion.  The  boats 
should  be  in  the  tube  during  the  heating  of  the  latter  in  a  stream 
of  oxygen. 

When  a  substance  contains  sulphur,  the  boat  in  the  rear  is 
pushed  to  within  6-7  cm.  of  the  contact  star,  but  when  sulphur  is 
not  present,  the  boat  is  kept  at  a  distance  of  8-10  cm.  from  the 
contact  star.  Under  these  conditions  the  heating  in  a  stream  of 
oxygen  (320-350°)  is  done  very  cautiously  in  the  course  of  at 
least  a  half  hour,  or  better  still,  a  whole  hour,  or  more.  The 
course  of  the  combustion  is  otherwise  the  same  as  that  described 
above.  A  rapid  current  of  oxygen  is  avoided  as  much  as  possible, 
otherwise  complete  absorption  by  lead  peroxide  will  be  prevented. 

Should  the  platinum  (star,  roll,  etc.)  come  in  contact  with  lead 
peroxide  or  minium  at  any  time,  the  particles  of  the  latter  are 
removed  first  mechanically,  and  then  by  the  use  of  hot  dilute 
hydrochloric  acid. 

If  a  substance  explodes  on  heating,  it  is  mixed  in  the  boat  with 
quartz-powder  or  quartz-sand  (previously  treated  with  hot  hydro- 
chloric acid  and  heated  to  glowing),  or  with  lead  chromate  which 
has  been  heated  to  redness. 

Simultaneous  Determination  of  Sulphur  with  Carbon  and  Hydro- 
gen.—  In  this  case  the  lead  peroxide-minium  mixture  should  nat- 
urally be  free  from  sulphates.  In  order  to  test  the  substance 
for  sulphuric  acid  20-25  grammes  of  the  mixture  is  digested  on  a 


126  GENERAL   PART 

water-bath  for  one  hour  with  a  20  %  solution  of  sodium  carbonate, 
free  from  sulphuric  acid.  The  mixture  is  crushed  and  stirred  fre- 
quently. It  is  then  filtered,  washed  with  50  c.c.  of  water,  and 
acidified  with  hydrochloric  acid.  The  hot  solution  is  now  treated 
with  barium  chloride.  The  liquid  should  remain  perfectly  clear, 
even  after  standing  overnight. 

At  the  end  of  the  combustion,  and  after  the  removal  of  the 
absorption  apparatus,  the  boats  are  carefully  drawn  out  by  the  use 
of  a  strong  copper  wire  with  a  little  hook  at  one  end.  The  sur- 
face of  the  substance  in  the  first  two  boats  will  be  covered  with  a 
white  layer  of  lead  sulphate.  The  contents  of  the  boats  are  trans- 
ferred into  a  beaker ;  the  empty  boats  are  placed  into  a  wide  test- 
tube  and  heated  on  a  water-bath  with  a  5  %  solution  of  pure 
sodium  carbonate  ;  the  liquid  is  added  to  the  main  portion  of  lead 
peroxide  and  the  boats  are  once  more  washed  with  a  dilute  solu- 
tion of  sodium  carbonate.  Traces  of  sulphuric  acid  may  also 
adhere  to  the  contact  substance,  the  roll,  the  combustion  tube 
and  the  inner  tube.  These  are,  therefore,  rinsed  freely  with  water. 
The  mouth  of  the  inner  tube  is  also  dipped  in  a  few  cubic  centi- 
metres of  water,  but  the  small  wash  bottle  is  not  removed.  If  the 
salt  of  a  sulphonic  acid  was  analysed  the  combustion  boat  is  also 
washed  with  water,  or  better  still,  it  is  treated,  with  the  boats, 
with  a  solution  of  sodium  carbonate.  In  this  case  the  wider  por- 
tion of  the  inner  tube  is  also  rinsed  with  water.  All  the  washings 
containing  sulphuric  acid  are  poured  into  the  beaker,  which  holds 
the  contents  of  the  boats.  The  mixture  should  give  an  alkaline 
reaction.  It  is  heated  over  an  actively  boiling  water-bath  for  at 
least  one  hour.  It  is  frequently  stirred,  and  the  precipitate  is 
crushed  with  a  glass  rod  which  has  been  flattened  out  at  one  end. 

The  sulphuric  acid  is  determined  quantitatively  as  barium  sul- 
phate by  one  of  the  following  two  methods  :  The  entire  liquid  is 
separated  from  the  precipitate  by  filtration.  The  latter  is  washed 
with  water.  Should  the  filtrate  show  turbidity  by  this  treatment,  it 
is  once  more  poured  through  the  same  filter.  The  clear  filtrate  is 
then  acidified  with  dilute  hydrochloric  acid,  and  is  finally  precipi- 
tated at  the  boiling  point  with  barium  chloride  by  the  usual  method. 


ORGANIC  ANALYTICAL   METHODS  I2/ 

The  second  method  is  that  proposed  by  Dennstedt.  The  con- 
tents of  the  beaker  (solution  and  precipitate)  are  transferred  into 
a  measuring  cylinder.  (The  beaker  must  be  rinsed.)  The  volume 
is  now  increased  to  a  convenient  round  number  by  the  addition 
of  water.  Suppose  the  volume  is  100  c.c.  Since  the  specific 
gravity  of  the  precipitate  is  about  7  (if  7  grammes  of  lead  peroxide 
were  used),  then  in  100  c.c.  of  the  mixture  we  have  i  c.c.  of  the 
precipitate  and  99  c.c.  of  the  liquid.  To  simplify  the  calculation 
another  cubic  centimetre  of  water  is  added  so  as  to  make  the 
liquid  volume  just  100  c.c.  An  aliquot  part  is  then  taken,  i.e. 
95  c.c.,  and  filtered  through  a  dry  filter  as  described  above. 
The  washings  from  the  precipitate  are  also  saved.  After  acidify- 
ing with  hydrochloric  acid,  the  sulphuric  acid  is  precipitated  as 
barium  sulphate.  From  the  quantity  of  barium  sulphate  in  95  c.c. 
of  the  liquid  the  amount  in  100  c.c.  is  calculated;  in  other  words, 
from  the  quantity  in  the  partial  volume  that  in  the  total  volume 
is  calculated. 

Determination  of  Sulphur  alone.  —  It  is  evident  that  the  method 
described  above  may  also  be  used  for  the  determination  of  sul- 
phur alone,  by  leaving  out  the  absorption  apparatus.  It  is,  how- 
ever, simpler  and  more  convenient  to  use  anhydrous  sodium  car- 
bonate as  an  absorption  medium,  in  place  of  lead  peroxide.  The 
boats  are  filled  with  pure,  calcined  sodium  carbonate  (free  from 
sulphuric  acid).  The  substance  is  gently  pressed  down  with  a 
spatula.  The  combustion  tube  containing  the  boats  is  heated  in 
a  stream  of  oxygen,  the  sodium  carbonate  being  heated  to  about 
400°  with  the  flame-tube.  The  absorption  apparatus  is  replaced 
by  a  straight  calcium  chloride  tube  which  is  connected  with  the 
palladium  bottle.  At  the  end  of  the  combustion  the  cooled  boats 
are  drawn  out  of  the  tube  by  means  of  a  bent  wire,  and  their  con- 
tents are  transferred  into  a  beaker.  The  boats  are  placed  in  a 
wide  test-tube  and  treated  with  hot  water.  The  liquid  is  added 
to  the  dry  sodium  carbonate.  The  combustion  tube,  the  platinum 
star,  the  inner  tube,  and  the  combustion  boat  are  rinsed  with  water. 
In  short,  the  process  described  above  is  exactly  followed.  In 
order  to  change  traces  of  sulphites  in  the  alkaline  solution  into 


I28  GENERAL   PART 

sulphates,  it  is  heated  and  then  treated  with  a  few  cubic  centi- 
metres of  a  saturated  solution  of  bromine  water.  The  beaker  is 
now  covered  with  a  watch  crystal,  and  the  solution  is  carefully 
acidified  (evolution  of  carbon  dioxide)  with  moderately  strong 
hydrochloric  acid.  The  solution  is  heated  until  the  yellow  colour, 
due  to  excess  of  bromine,  disappears.  It  is  then  treated  hot  with 
barium  chloride. 

This  method  is  so  easy  and  convenient  after  a  few  trials,  that  it 
seems  to  be  destined  to  finally  replace,  the  Carius  method.  The 
analysis,  including  the  weighing  of  the  barium  sulphate,  may  be 
usually  completed  without  difficulty  in  half  a  day.  The  method 
has  the  further  advantage  over  Carius'  method  that  whereas  in  the 
latter  oxidation  is  sometimes  incomplete  with  substances  like 
sulphonic  acids  or  sulphones,  the  difficulty  is  not  experienced  in 
this  method.  If  a  sufficient  quantity  of  the  substance  is  on  hand, 
it  is  much  more  advantageous  to  carry  on  a  separate  determina- 
tion for  sulphur  by  the  sodium  carbonate  method,  and  ignore  the 
results  from  lead  peroxide  in  the  simultaneous  determination  of 
sulphur,  carbon  and  hydrogen. 

If  the  substance  contains  a  small  percentage  of  sulphur,  the 
addition  of  barium  chloride  may  not  precipitate  barium  sulphate, 
even  after  long  heating,  due  to  the  solubility  of  the  latter  in  excess 
of  barium  chloride.  But  the  precipitate  will  form  when  the  solu- 
tion is  allowed  to  stand  overnight.  If  a  larger  quantity  of  sulphur 
is  present,  and  a  precipitate  forms  as  soon  as  barium  chloride  is 
added,  the  precipitate  is  filtered  in  the  usual  way,  after  the  solu- 
tion has  become  clear.  The  filtrate  is  then  allowed  to  stand  for  a 
day  so  as  to  recover  any  precipitate  that  may  form.  The  same 
procedure  is  also  followed  in  the  lead  peroxide  method. 

Analysis  of  Substances  containing  a  Halogen.  —  If  an  organic 
substance  contains  a  halogen  in  addition  to  carbon,  hydrogen  and 
oxygen  (but  no  nitrogen  or  sulphur),  a  simultaneous  determina- 
tion of  carbon,  hydrogen  and  halogen  may  be  carried  out  by  the 
use  of  "  molecular  silver  "  (Kahlbaum).  A  long  porcelain  boat  is 
filled  with  a  few  grammes  of  molecular  silver.  During  the  heating 
of  the  combustion  tube  this  is  also  heated  by  the  flame-tube,  a 


ORGANIC   ANALYTICAL   METHODS  I2Q 

somewhat  higher  temperature  being  used  than  that  prescribed  for 
lead  peroxide. 

The  warm  boat  is  then  removed  and  transferred  into  a  weighing 
tube  (preferably  a  tube  with  two  short  legs  near  the  open  end), 
and  is  weighed  after  cooling.  During  the  combustion  the  boat  is 
kept  at  a  distance  of  about  6  cm.  from  the  contact  star,  and  is 
heated  to  300-350°  with  the  flame-tube.  At  the  end  of  the 
analysis  the  weight  of  the  silver  boat  gives  directly  the  amount  of 
halogen  in  the  substance. 

Halogen  compounds,  and  especially  compounds  very  rich  in 
halogen,  burn  much  more  slowly  than  halogen- free  substances. 
On  this  account  they  easily  distil  over  the  contact  star  without 
decomposition,  and  the  typical  glow  of  the  platinum,  as  well  as 
.  the  blackening  of  the  tube,  are  not  noticed.  When  this  is  the 
case  the  combustion  is  carried  out  very  carefully  and  slowly,  and 
the  oxygen  is  not  allowed  to  stream  too  rapidly. 

The  method  described  above  cannot  be  used  directly  if  the 
halogen  compound  contains  nitrogen  or  sulphur,  due  to  the  forma- 
tion of  silver  nitrite  and  silver  nitrate  or  silver  sulphate.  For  the 
determination  of  halogen  in  this  case,  as  well  as  the  determination 
of  sulphur  and  halogen  (by  the  use  of  lead  peroxide)  see  Prof.  Dr. 
M.  Dennstedt's  "Anleitung  zur  vereinfachten  Elementaranalyse  " 
(Hamburg,  Otto  Meissners  Verlag,  2.  Aufl.,  1906). 

Calculation  of  the  Atomic  Formula.  —  In  order  to  calculate  the 
simplest  formula  of  a  substance  from  the  figures  giving  its  per- 
centage composition,  the  method  is  as  follows  :  If  a  subtance 
contains,  e.g. : 

Carbon  =  48.98  % 
Hydrogen  =  2.72  % 
Chlorine  =  48.30  % 

the  percentage  figures  are  divided  by  the  corresponding  atomic 
weights.     There  is  thus  obtained  : 


48.98 -r- 1 2  =4.o8C 
2.72  -5-  i  =  2.72  H 
8.0-5--  =  J-6  Cl 


130  GENERAL  PART 

These  figures  are  divided  by  the  smallest  —  in  this  case  1.36  : 

4.08-^-  1.36  =  3  C 
2.72  -s-  1.36  =  2  H 
1.36^-  1.36  =  i  Cl 

The  simplest  atomic  formula,  therefore,  is  C3H2C1.  If  the  num- 
bers obtained  in  the  last  division  are  not  integers,  they  are  multi- 
plied by  the  smallest  integer  which  will  convert  the  fractions  into 
whole  numbers.  If,  e.g.,  the  following  numbers  have  been  found, 
1.25,  1.75,  and  0.5,  they  are  multiplied  by  4,  the  results  being 
5,  7,  and  2. 

The  simplest  formula  thus  obtained  from  the  analytical  data 
does  not  always  correspond  with  the  true  molecular  weight.  This 
must  be  determined  by  one  of  the  usual  methods,  unless  it  may 
be  inferred  from  the  nature  of  the  reaction  by  which  the  sub- 
tance  analysed  was  produced. 

The  exact  atomic  weights  of  the  elements  used  in  analytical 
calculations  are  : 

H  =      1.008 

C    =      I2.OO 

N  =  14.01 
S  =  32.07 
Cl=  35-46 
Br  —  79.92 
I  =  126.92 
O  =  16.00 

These  figures  are  taken  from  Kuster's  "  Logarithmischen  Rechen^ 
tafeln  fur  Chemiker." 


SPECIAL   PART 


I.   ALIPHATIC   SERIES 

i.  REACTION:  THE  REPLACEMENT  OF  AN  ALCOHOLIC  HYDROXYI 
GROUP  BY  A  HALOGEN 

I .    EXAMPLE  :   Ethyl  Bromide  from  Ethyl  Alcohol l 

To  200  grammes  (noc.c.)  of  concentrated  sulphuric  acid  con- 
tained in  a  round  litre-flask,  add  quickly  with  constant  shaking, 
without  cooling,  90  grammes  of  alcohol  (about  95%).  After 
cooling  the  mixture  to  the  room  temperature,  add  carefully  75 
grammes  of  ice-water,  the  cooling  being  continued,  and  then  100 

grammes  of  finely  pul- 
verised potassium  bro- 
mide (see  Hydrobromic 
Acid,  page  379).  The 
mixture  is  subjected  to 
distillation,  which  must 
not  be  too  slow,  the  flask 
being  heated  on  a  small 
sand-bath  with  a  large 
flame  (Fig.  63).  Since 
the  boiling-point  of  ethyl 
bromide  is  low  (38°),  a 
long  condenser,  with  a 
quite  rapid  current  of  water  passing  through  it,  is  used.  An  up- 
right coil  condenser  (see  Fig.  27,  page  34)  may  be  employed 
advantageously.  At  the  beginning  of  the  operation,  the  receiver 
is  filled  with  a  sufficient  amount  of  water  containing  a  few  pieces 
of  ice  to  allow  the  end  of  the  adapter  to  dip  under  the  surface. 
The  reaction  is  ended  as  soon  as  the  oily  drops  which  sink  to  the 
bottom  of  the  receiver  cease  passing  over.  If,  during  the  distilla- 
tion, the  contents  of  the  receiver  should  be  drawn  up  into  the  con- 
ij.  1857,441.  131 


FIG.  63. 


132  SPECIAL   PART 

denser,  this  difficulty  may  be  overcome  by  placing  the  receiver 
in  such  a  position  that  the  end  of  the  adapter  reaches  just  below 
the  surface  of  the  water.  The  same  result  may  be  attained  by  turn- 
ing the  adapter  to  one  side,  so  that  air  may  enter  it.  The  lower 
layer  of  the  distillate  consisting  of  ethyl  bromide  is  washed  in  the 
receiver  several  times  with  water,  and  finally  with  a  dilute  solution 
of  sodium  carbonate,  during  which  the  flask  must  not  be  closed. 
The  lower  layer  is  then  run  out  of  a  separating  funnel,  dried  with 
calcium  chloride,  and  finally  distilled,  the  same  precautions  as  to 
cooling,  mentioned  above,  being  observed.  In  this  case  a  very 
small  flame  of  a  microburner  is  used,  or  the  burner  tube  of  a 
Bunsen  burner  is  removed  and  a  luminous  flame,  a  few  millimetres 
high,  is  lighted  at  the  nozzle.  The  ethyl  bromide  distils  between 
35-40°,  the  main  portion  at  38-39°.  In  consequence  of  the  low 
boiling-point  of  ethyl  bromide,  it  is  never  allowed  to  stand  in  open 
vessels  for  any  length  of  time ;  during  the  drying  over  calcium 
chloride,  the  flask  must  be  closed  by  a  tight-fitting  cork.  The 
finished  preparation,  particularly  at  summer  temperature,  must 
not  be  preserved  in  thin-walled  vessels  of  any  kind,  but  always  in 
thick-walled,  so-called  specimen  bottles.  Yield,  70-80  grammes. 
At  the  conclusion  of  this  experiment,  as  well  as  in  all  the  follow- 
ing preparations,  the  amount  of  actual  yield  is  compared  with  the 
percentage  required  by  theory.  The  following  points  are  there- 
fore noted :  According  to  the  chemical  equation,  one  molecular 
weight  of  potassium  bromide  (119)  requires  one  molecular  weight 
of  alcohol  (46).  In  actual  work,  especially  in  a  large  number  of 
organic  reactions  which  do  not  take  place  quantitatively,  and 
where  economy  is  to  be  considered,  one  of  the  reacting  substances 
is  taken  in  excess,  in  accordance  with  the  Law  of  Mass  Action. 
Since  the  price  of  one  kg.  of  potassium  bromide  is  about  4 
marks,  and  that  of  one  kg.  of  alcohol  (including  duty)  is  about 
i. 80  marks, —  duty-free  alcohol  0.90  mark,  —  the  price  of  one 
molecule  of  potassium  bromide  (119  x  4)  compared  with  that  of 
one  molecule  of  alcohol  (including  duty)  (46  X  1.80),  or  duty- 
free  alcohol  (46  x  0.90),  is  in  the  ratio  of  6  :  i,  or  12  :  i.  From 
the  standpoint  of  economy  it  is  more  rational  to  use  an  excess 


ALIPHATIC   SERIES  133 

of  the  cheaper  alcohol  and  convert  the  more  expensive  potassium 
bromide,  as  completely  as  possible,  into  ethyl  bromide.  The 
quantities  used  in  the  above  experiment  are  in  accordance  with 
these  considerations.  100  grammes  of  potassium  bromide  require 
theoretically  39  grammes  of  alcohol,  while  the  quantity  of  alcohol 
used  is  86  grammes  (90  grammes  of  95  %),  i.e.  more  than  twice 
the  theoretical  amount.  In  order  to  calculate  the  yield  theoreti- 
cally possible,  the  quantity  of  potassium  bromide  must  be  taken  as 
the  basis,  since  the  conversion  of  the  total  amount  of  alcohol  into 
ethyl  bromide  is  impossible.  When  the  alcohol  used  for  the  prepa- 
ration of  its  corresponding  bromide  is  more  expensive  than  potas- 
sium bromide,  then  the  substance  to  be  taken  in  excess  is  naturally 
potassium  bromide.  (Compare  the  discussion  of  the  Law  of  Mass 
Action  under  Acetic  Ester.) 

The  ethyl  bromide  thus  obtained  is  contaminated  with  a  small 
amount  of  ether.  If  it  be  desired  to  remove  this,  the  well-cooled 
crude  ethyl  bromide,  contained  in  a  flask  surrounded  by  a  freezing 
nixture  of  ice  and  salt,  is  treated,  before  drying  with  calcium 
chloride,  with  concentrated  sulphuric  acid,  added  drop  by  drop 
and  with  frequent  shaking,  until  it  separates  out  in  a  layer  under 
the  ethyl  bromide.  The  acid  containing  the  dissolved  ether  is 
then  run  off  (in  a  separating  funnel)  from  the  ethyl  bromide,  which 
is  shaken  up  several  times  with  ice  water,  dried  with  calcium  chlo- 
ride, and  redistilled  as  before.  For  the  preparation  of  ethyl  ben- 
zene (which  see)  the  ethyl  bromide  need  not  be  thus  purified. 

2.    EXAMPLE  :  Ethyl  Iodide  from  Ethyl  Alcohol l 

To  a  mixture  of  5  grammes  of  red  phosphorus  and  40  grammes 
of  absolute  alcohol,  contained  in  a  small  flask  of  about  200  c.c. 
capacity,  50  grammes  of  finely  pulverised  iodine  are  added  gradu- 
ally in  the  course  of  a  quarter  hour  ;  the  flask  is  frequently  shaken 
during  the  addition,  and  cooled  from  time  to  time  by  immersion 
in  cold  water.  An  air  condenser  —  a  straight  vertical  glass  tube 
is  the  common  form  —  is  connected  with  the  flask,  and  the  reac- 

1  A.  126,  250. 


134  SPECIAL   PART 

tion  mixture  is  allowed  to  stand  at  least  four  hours.  (In  czce  the 
experiment  was  begun  late  in  the  afternoon,  it  may  stand  until 
the  next  day.)  In  order  to  complete  the  reaction,  the  mixture  is 
heated  for  two  hours  on  the  water-bath,  a  reflux  condenser  being 
attached  to  the  flask.  The  ethyl  iodide  is  then  distilled  off  conven- 
iently by  immersing  the  flask  in  a  rapidly  boiling  water-bath.  The 
distillation  is  facilitated  by  the  use  of  a  frayed  thread  (see  page  34). 
Should  the  last  portions  go  over  with  difficulty,  the  water-bath  is 
removed,  the  flask  is  dried  and  heated  for  a  short  time  with  a 
luminous  flame  kept  in  constant  motion.  The  distillate,  coloured 
brown  by  iodine,  is  washed  several  times  with  water  to  free  it  from 
alcohol,  and  then  with  water  to  which  a  few  drops  of  caustic  soda 
have  been  added,  to  remove  the  iodine ;  the  colourless  oil  is  now 
separated  in  a  dropping  funnel,  dried  with  a  small  quantity  of 
granular  calcium  chloride,  and  distilled.  If  the  calcium  chloride 
should  float  on  the  oil,  it  is  poured  through  a  funnel  containing 
some  asbestos  or  glass-wool  into  the  fractionating  flask.  The  boil- 
ing-point of  ethyl  iodide  is  72°.  Yield,  about  50  grammes. 

The  following  questions  are  to  be  answered  at  this  point  :  Which 
one  of  the  reacting  substances  was  taken  in  excess  ?  Why  ?  What 
percentage  of  the  theoretical  yield  of  ethyl  iodide  is  obtained  ? 

Both  of  these  reactions  are  special  cases  of  a  reaction  of  general 
application,  viz.  :  the  replacement  of  an  alcoholic  hydroxyl  group  with 
a  halogen  atom.  This  may  be  effected  in  two  ways  :  (i)  by  causing 
the  alcohol  to  react  with  the  halogen  hydracid  as  in  the  preparation 
of  ethyl  bromide,  e.g. : 


C2H-  .  |QH  +  Hj  Br  =  H2O  +  C2H5  .  Br 
(HC1,  HI) 

(2)  by  treating  the  alcohol  with  a  phosphorus  halide,  as  in  the  prepara- 
tion of  ethyl  iodide,  e.g.: 

3  C2H5 .  OH  +  PI3  =  3  C2H5  . 1  +  P(OH)3 
(PC13,  PBr3) 

i .  The  first  reaction  takes  place  most  easily  with  hydriodic  acid  ;  in 
many  cases  saturation  with  the  gaseous  acid  being  sufficient  to  induce 
the  reaction.  Hydrobromic  acid  reacts  with  greater  difficulty ;  it  is 


ALIPHATIC  SERIES  135 

frequently  necessary  to  heat  the  alcohol  saturated  with  the  acid  in  a 
sealed  tube.  The  above  method  for  the  preparation  of  ethyl  bromide 
is  a  simple  case  of  the  general  reaction.  In  place  of  using  hydrobromic 
acid  directly,  it  can  in  some  cases,  like  the  one  given,  be  generated  by 
warming  a  mixture  of  potassium  bromide  and  sulphuric  acid : 

KBr  +  H2SO4  =  HBr  +  KHSO4. 

Hydrochloric  acid  reacts  with  most  difficulty,  and  it  is,  e.g.,  in  the  prepa- 
ration of  methyl  chloride  and  ethyl  chloride,  necessary  to  employ  a 
dehydrating  agent  —  zinc  chloride  is  the  best  —  or  with  the  alcohols  of 
high  molecular  weights,  to  heat  in  a  closed  vessel  under  pressure. 

This  reaction  is  not  only  applicable  to  the  aliphatic,  but  also  to  the 
aromatic  alcohols  ;  e.g. : 

C6H5  .  CH2 .  OH  +  HC1  =  CGH5 .  CH2C1  +  H2O 

Benzyl  alcohol  Benzyl  chloride 

But  phenol  hydroxyl  groups  cannot  be  replaced  by  the  action  of  a 
halogen  hydracid. 

With  di-acid  and  poly-acid  alcohols  the  reaction  takes  place,  at  least 
with  hydrochloric  and  hydrobromic  acids  ;  but,  in  this  case,  the  number 
of  hydroxyl  groups  which  are  replaced  by  the  halogen  depends  upon 
the  conditions  of  the  experiment,  the  quantity  of  the  halogen  acid,  the 
temperature,  etc.,  e.g. : 

CH2.OH  CH2.Br 


+  HBr  =  \  +  H20 

CH2.OH  CH2.OH 

Ethylene  glycol  Ethylene  bromhydrine 

CH2.OH  CH2.OH 

CH.OH    +2HC1    =CHC1        +2H2O 
CH2.OH  CH2C1 

Glycerol  Dichlorhydrine 


CH2.OH  CH2.Br 

CH2  -f2HBr   =CH2  +  2  H2O 

CH2.OH  CH2.Br 

Trimethylene  glycol  Trimethylene  bromide 

Hydriodic  acid,  in  consequence  of  its  reducing  properties,  acts  upon  the 
poly-acid  alcohols  in  a  different  manner.  A  single  hydroxyl  group,  and 
that  particular  one  in  combination  with  a  carbon  atom  which  is  in  turn  in 
combination  with  other  carbon  atoms,  is  replaced  by  iodine,  while  at  times 
other  hydroxyl  groups  are  replaced  by  the  hydrogen  of  the  acid,  e.g. : 


C 


SPECIAL  PART 

CH2.OH  CH3 

CH .  OH  +  5  HI  =  CHI  +  3  H2O  -f  4 1 
;H2.OH  CH3 

Glycerol  Isopropyl  iodide 

CH2(OH).CH(OH).CH(OH).CH2(OH)  +  7HI 

Erythrite 

=  CH3.CH2.CHI.CH3  +  4H2O  +  6I 

«-Sec.  Butyl  iodide 

CH2(OH).CH(OH).CH(OH).CH(OH).CH(OH).CH2(OH)+  uHI 

Ma  unite 

=  CH3.CHI.CH2.CH2.CH2.CH3  +  6H20  +  10! 

«-Sec.  Hexyl  iodide 

With  derivatives  of  alcohols,  e.g.  alcohol-acids   (hydroxy  acids)   the 

first  reaction  takes  place : 

CHo.  OH  .  CH, .  COOH  +  HI  =  CHJ  .  CH2 .  COOH  +  H2O 


j3-Hydroxyproprionic  acid  £-Iodoproprionic  acid 

CH2(OH).  CH(OH).  COOH  +  2  HC1  =  CH2C1  .  CHC1  .  COOH  +  2  H2O 

Glyceric  acid  a-/3-Dichlorproprionic  acid 

2.  The  second  reaction  takes  place  much  more  energetically,  espe- 
cially when  a  phosphorus  halide  which  has  been  previously  made  is 
used.  This  is  not  always  necessary,  at  least  in  introducing  bromine 
and  iodine;  in  many  cases  it  is  better  to  generate  the  phosphorus  halides 
in  the  course  of  the  reaction,  by  adding  to  the  mixture  of  alcohol  and 
red  phosphorus  either  bromine  from  a  dropping  funnel,  or  as  above, 
finely  pulverised  iodine.  This  reaction,  as  well  as  the  first,  is  applicable 
to  poly-acid  alcohols  and  substituted  alcohols,  e.g.  : 

(a)  CH2(OH)  .  CHS(OH)  +  2  PCI.  =  CH2C1  .  CH2C1  +  2  FOCI,  +  2  HC1 

Ethylene  glycol  Ethylene  chloride 

(b)  CH2(OH)  .  CHC1  .  CH2C1  +  PC15 

Dichlorhydrine 

=  CH2C1  .  CHC1  .  CH,C1  +  POC13  +  HC1 

Trichlorhydrine 

This  example  illustrates  the  more  energetic  action  of  the  phosphorus 
halide  as  compared  with  the  corresponding  hydrogen  halide  ;  it  is  im- 
possible to  replace  the  third  hydroxyl  group  of  glycerol  with  chlorine 
by  the  use  of  hydrochloric  acid. 

(0  CH,  .  CH(OH).  COOH  +  PC15  =  CHo  .  CHC1  .  COOH  +  POC1.,  +  HC1 

(1)  (I) 

a-Hydroxyproprionic  acid  a-Chlorproprionic  acid 

In  cases  of  this  kind  a  complication  arises,  due  to  the  fact  that  the 
phosphorus  halide  also  acts  upon  the  hydroxyl  of  the  carboxyl  group, 
replacing  it  with  the  halogen,  giving  rise  to  an  acid-chloride  : 


ALIPHATIC   SERIES  137 

CH3 .  CHC1 .  CO .  OH  +  PC13  =  CHo .  CHC1 .  CO .  Cl  +  POC1,  +  HC1 

The  acid  may  be  regenerated  by  treating  the  acid-chloride  with  water: 

CH3 .  CHC1 .  CO .  Cl  +  H3O  =  CH3 .  CHC1 .  CO .  OH  +  HC1 

The  action  of  phosphorus  iodide  on  poly-acid  alcohols  is  similar  to  the 
action  of  hydriodic  acid  referred  to  under  Reaction  i . 

The  more  energetic  action  of  the  phosphorus  halides  may  also  be 
perceived  in  the  fact  that  phenol  hydroxyl  groups  can  be  replaced  by  a 
halogen,  by  the  use  of  the  phosphorus  compounds,  which,  as  mentioned 
above,  is  impossible  with  the  halogen  hydracids,  e.g. : 

CGH5 .  OH  +  PC15          =  C6H5 .  Cl  -f  POC13  +  HC1 

'  Phenol  (Br)  (Br) 

39  /NO2 

-f  PC15  =  C6H4<         +  POC13  +  HC! 
OH  \C1 


/OH  /Cl 

,H0<f  -f  PCL  =  CfiH9<f 


C6H2<  +  PC15  =  C6H2<T  +  POC13  +  HC1 

XNO2)3  '     XN°2)s 

Picric  acid  Picryl  chloride 

But  the  quantities  obtained  are  much  less  satisfactory,  the  reason  being 
that  the  phosphorus  oxychloride  attacks  the  unacted-upon  phenol,  form- 
ing phosphoric  acid  esters,  e.g.: 

POC13  +  3  C6H5.OH  =  PO.  (OQH5),  +  3  HC1 

In  this  way  a  large  portion  of  the  phenol  is  withdrawn  from  the  main 
reaction. 

The  monohalogen  alkyls  CnH(2n+i)Cl(Br,  I)  are  in  most  cases  colour- 
less liquids,  the  exceptions  being  methyl  and  ethyl  chlorides  and  methyl 
bromide,  which  are  gaseous  at  the  ordinary  temperature,  and  the  mem- 
bers of  the  series  having  high  molecular  weights,  like  cetyl  iodide, 
C1BH33I,  which  are  semi-solid,  salve-like  substances.  The  iodides  are 
only  colourless  when  freshly  prepared ;  on  long  standing,  especially 
under  the  influence  of  light,  a  slight  decomposition,  resulting  in  the 
separation  of  iodine,  takes  place,  imparting  to  them  a  faint  pink  colour 
at  first,  which  becomes  brownish  red  after  a  long  time.  This  decom- 
position can  be  prevented  if  some  finely  divided,  so-called  molecular 
silver  is  added  to  the  liquid.  A  coloured  iodide  can  be  made  colourless 
by  shaking  it  with  some  caustic  soda  solution.  The  halogen  alkyls 
mix  readily  with  organic  solvents,  as  alcohol,  ether,  carbon  disulphide, 


138 


SPECIAL   PART 


benzene,  etc.,  but  not  with  water.  The  chlorides  are  lighter,  the  bro- 
mides and  iodides  heavier  than  water;  the  latter  have  the  highest 
specific  gravities.  This  property  decreases  in  all  three  classes  with  the 
decrease  in  halogen  percentage  from  the  lower  up  to  the  higher  mem- 
bers of  the  series  ;  i.e.  the  higher  molecular  weight  compounds  have  a 
smaller  specific  gravity  than  the  lower  members.  The  chlorides  have 
the  lowest  boiling-points  ;  the  corresponding  bromides  boil  about  25°, 
and  the  iodides  50°  higher. 

The  ease  with  which  the  monohalogen  alkyls  react  with  other  com- 
pounds gives  them  great  importance  ;  they  are  used  primarily  as  a  means 
of  introducing  alkyl  groups  into  other  molecules,  i.e.  by  replacing  an 
hydrogen  atom  with  an  alkyl  group.  If  it  is  desired,  e.g.,  to  replace  in 
an  alcohol,  mercaptan,  phenol,  or  acid  the  hydrogen  of  the  (OH)-, 
(SH)-,  or  (COOH)  -group  by  an  alkyl  radical,  i.e.  to  prepare  an  ether,  or 
ester  of  these  substances,  the  corresponding  sodium  compound,  or  in 
case  of  acids,  better  the  silver  salt,  is  treated  with  the  halogen  alkyl,  e.g.  ; 

C2H5  .  ONa  +  IC2H5  =  C2H5  .  0  .  C2H5  +  Nal 

Sodium  alcoholate  Ethyl  ether 

C2H5  .  SNa  +  IC2H5  =  C2H5  .  S  .  C2H5  +  Nal 

Sodium  ethyl  mercaptide  Ethyl  sulphide 

QH5  .  ONa  +  ICHo  =  C6H5  .  0  .  CH3  +  Nal 

Sodium  phenolate  Phenyl  methyl  ether 

=  Anisol 

CH3  .  COOAg  +  IC2H3  =  CH3  .  COO  .  C2H5  +  Agl 

Silver  acetate  Ethyl  acetate 

The  alkyl  groups  may  be  introduced  into  the  ammonia  molecule  and 
into  organic  amine  molecules  by  means  of  the  halogen  alkyls  ;  e.g.  : 


NH,  +  ICHo  =  NH2.CH3  +  HI 

Methyl  amine 

Di-  and  tri-methyl  amine  are  also  formed  at  the  same  time. 
C6H5.  NH2  +  2  CH3C1  -  C6HS.  N(CH3)2  +  2  HC1. 

Aniline  Dimethyl  aniline 

Hydrogen  atoms  in  combination  with  carbon  may  also  be  replaced  by 
alkyl  radicals,  by  means  of  the  halogen  alkyls.  Since  under  these  con- 
ditions another  radical  is  introduced  into  the  molecule,  it  presents  a 
method  of  preparing  the  higher  members  of  a  series  from  the  lower. 
simpler  ones.  Various  examples  of  this  will  be  taken  up  later  in  labor 


ALIPHATIC  SERIES  139 

atory  practice.     Here  it  will  be  sufficient  to  refer  to  several  equations 
showing  this  kind  of  reaction. 

CH3 .  CO .  CHNa .  COOC2H5 + ICH3  =  CH3 .  CO .  CH  -  COOC2H5  +  Nal 

Sodium  acetacetic  ester 

CH3 

Methylacetacetic  ester 

COOC2H6  COOC2H5 

:HNa        +  IC2H5  =  CH  -  C2H5  +  Nal 
"OOC2H5  COOC2H5 

Sodium  malonic  ester  Ethyl  malonic  ester 

C6H6  -f  C1C2H5        =  C6H5 .  C2H5  +  HC1 

Benzene  Ethyl  benzene 

(In  presence  of  A1C13) 

Fittig's  Synthesis,  to  be  taken  up  later,  is  a  case  of  this  kind,  by 
which  a  halogen  atom  is  replaced  by  an  alkyl  group ;  e.g. : 

C6H5Br  +  BrC2H5  +  2  Na  =  C6H5. C2H5  +  2  NaBr 

Brom  benzene  Ethyl  benzene 

Further,  the  halogen  alkyls  serve  for  the  preparation  of  the  unsatu- 
rated  hydrocarbons  of  the  ethylene  series. 

CH, .  CHI .  CH,  =  CH, .  CH  =  CH9  +  HI 


Isopropyfr  iodide  Propylene 

In  many  cases  the  alcohols  may  also  be  prepared  from  the  halogen 
alkyls  ;  e.g.  : 

CH8.CHI.CH3  +  HOH  =  CH3.CH(OH).CH3  +  HI 

Isopropyl  alcohol 

This  reaction  is  obviously  only  of  importance  when  the  halogen  alkyl 
is  not  obtained  from  the  corresponding  alcohol,  as  is  the  case  in  the 
example  given.  As  above  mentioned,  the  isopropyl  iodide  is  most 
simply  obtained  from  glycerol  and  hydriodic  acid,  so  that  by  this 
reaction  the  glycerol  can  be  converted  into  the  isopropyl  alcohol 
(compare  Reaction  13).  Halogen  alkyls  also  unite  directly  with  other 
compounds,  like  sulphides  and  tertiary  animes  : 


9r 
M 

Ethyl  sulphide  Triethylsulphine  iodide 


140  SPECIAL  PART 

N(CH3)3  +  CHgCl  =  N(CH3)4C1 

Trimethyl  amine     Tetramethyl  ammonium  chloride 

C5HRN  +  ICH8  -  C5H,N  •  ICH3 

Pyridine  Methylpyridine  iodide 

With  these  examples  the  list  of  the  many-sided  reactions  of  the  hal- 
ogen alkyls  is  not  exhausted ;  they  are  also  used  for  the  preparation 
of  the  metallic  alkyls,  e.g.  zinc  alkyls ;  for  the  preparation  of  the 
phosphines,  and  for  many  other  compounds.  Through  the  Grignard 
reaction,  with  its  many-sided  applications,  the  halogen  alkyls  have  re- 
cently become  extremely  important.  Finally,  attention  is  called  to  the 
characteristic  difference  between  the  organic  and  inorganic  halides. 
While,  e.g.,  potassium  chloride,  bromide,  or  iodide  in  solution  act 
instantly  with  a  silver  nitrate  solution  to  form  a  quantitative  precipitate 
of  silver  chloride,  bromide,  or  iodide  respectively,  silver  nitrate  in  a 
water  solution  does  not  act  on  most  organic  halides,  so  that  this  reagent 
does  not  serve  in  the  usual  way  to  show  the  presence  of  a  halogen. 

EXPERIMENT  :  Treat  a  solution  of  silver  nitrate  with  a  few  drops 
of  ethyl  bromide.  Not  the  least  trace  of  silver  bromide  is  formed. 

It  has  been  customary  to  explain  this  by  saying  that  the  affinity 
between  the  halogen  atom  and  carbon  is  greater  than  that  between  the 
halogen  and  the  metallic  atom.  According  to  our  later  views  the  differ- 
ence between  the  two  classes  of  compounds  is  explained  thus :  The 
metallic  halides  belong  to  the  class  of  so-called  electrolytes,  i.e.  sub- 
stances which  are  dissociated  in  water  solution,  e.g.  the  molecule  KC1 

is  dissociated  into  its  ions,  K  and  Cl.     The  organic  halides  are  non- 

•f 

electrolytes,  i.e.  the  solutions  of  these  contain  the  undissociated  mole- 
cules. According  to  this  conception,  the  potassium  chloride  reacts 
with  silver  nitrate,  because  no  further  separation  of  the  potassium  from 
the  chlorine  (other  than  that  effected  by  solution)  is  necessary,  while  in 
case  of  the  brom  alkyls,  the  brom-carbon  union  must  first  be  severed. 
Only  halogen  ions  react,  at  once,  quantitatively  with  the  silver  ions  of 
silver  nitrate. 

Ethyl  iodide  is  an  exception ;  when  shaken  with  a  solution  of  silver 
nitrate,  it  gives  an  abundant  precipitate  of  silver  iodide.  Other  iodides, 
especially  tertiary  iodides,  do  not  react  with  a  water  solution  of  silver 
nitrate,  as  readily  as  ethyl  iodide.  Methyl  and  ethyl  iodides  react 
quantitatively  when  an  alcoholic  solution  of  silver  nitrate  is  used.  The 
reaction  is  employed,  according  to  Zeisel,  for  the  determination  of 
methoxyl  groups.  Ethyl  bromide  reacts  with  alcoholic  silver  nitrate  on 
heating;  ethyl  chloride  reacts  more  slowly. 


ALIPHATIC  SERIES 


141 


2.   REACTION:   PREPARATION  OF  AN  ACID-CHLORIDE  FROM  THE 

ACID 

EXAMPLE  :    Acetyl  Chloride  from  Acetic  Acid l 

To  100  grammes  of  glacial  acetic  acid  contained  in  a  fraction- 
ating flask  connected  with  a  condenser  (coil  condenser),  80 
grammes  of  phosphorus  trichloride  are  added  through  a  dropping 
funnel,  the  flask  being  cooled  by  water.  The  bulb  is  then  im- 


FIG.  64. 

mersed  in  a  porcelain  dish  filled  with  v/ater  at  a  temperature  of 
40-50°,  and  the  heating  continued  until  the  active  evolution  of 
hydrochloric  acid  gas  slackens,  and  the  liquid  which  was  homo- 
geneous before  heating  has  separated  into  two  layers.  To  sepa- 
rate the  acetyl  chloride  which  forms  the  upper,  lighter  layer,  from 
the  heavier  layer  of  phosphorous  acid,  the  mixture  is  heated  on  a 

1  A.  87, 63. 


142 


SPECIAL   PART 


rapidly  boiling  water-bath  until  nothing  more  passes  over.  Since 
acetyl  chloride  is  very  easily  decomposed  by  moisture,  the  distillate 
must  not  be  collected  in  an  open  receiver,  but  the  condenser-tube 
must  be  tightly  connected  with  a  tubulated  flask  (suction  flask), 
protected  from  the  air  by  a  calcium  chloride  tube,  as  represented 
in  Fig.  64.  For  complete  purification,  the  distillate  is  distilled  in 
a  similar  apparatus,  except  that  the  dropping  funnel  is  replaced  by 
a  thermometer.  The  apparatus  represented  in  Fig.  17,  page  21, 
may  be  used  for  the  redistillation.  The  portion  distilling  from 
50-56°  is  collected  in  a  separate  vessel.  Boiling-point  of  pure 
acetyl  chloride,  51°.  Yield,  80-90  grammes. 

In  order  to  replace  the  hydroxyl  of  a  carboxyl  group  (CO  .  OH)  by 
chlorine,  a  reaction,  similar  to  the  one  employed  above  for  the  substi- 
tution of  an  alcoholic  hydroxyl  group  by  a  halogen,  may  be  used.  If, 
e.g.,  a  mixture  of  an  acid  and  phosphoric  anhydride  is  treated  with 
gaseous  hydrochloric  acid  (heating  if  necessary),  there  is  formed  an 
acid-chloride,  the  reaction  being  analogous  to  that  by  which  ethyl 
bromide  was  prepared. 

X.CO.OH  +  HC1  =  X.CO.C1  +  H20 

This  reaction  is  without  practical  importance,  since  the  reactions  in- 
volved in  the  methods  described  under  (2),  page  136,  take  place  much 
more  smoothly  and  easily,  and,  therefore,  are  exclusively  used.  In 
practice,  the  acid-chlorides  are  almost  always  prepared  by  the  action  of 
phosphorus  tri-  or  penta-chloride  on  the  acid  directly,  or  in  many  cases, 
on  the  sodium  or  potassium  salt.  Phosphorus  oxychloride  is  employed 
in  rare  cases.  The  selection  of  the  chloride  of  phosphorus  depends 
upon(i)  the  ease  with  which  the  acid  under  examination  reacts,  and 
(2)  upon  the  boiling-point  of  the  acid-chloride.  If,  as  in  the  case  of 
acetic  acid  and  its  homologues,  the  trichloride  of  phosphorus  reacts 
easily  with  the  formation  of  the  acid-chloride,  this  is  selected  in  prefer- 
ence to  the  more  energetic  pentachloride.  The  reaction  probably  takes 
place  in  accordance  with  the  following  equation  : 

3  CH;5 .  CO  .  OH  +  2  PC13  =  3  CH3 .  CO  .  Cl  +  P2O3  +  3  HC1 

The  quantity  of  acetic  acid  used  is  made  the  basis  for  the  calculation  of 
the  yield  required  by  theory. 

In  cases  in  which  the  boiling-point  of  the  acid-chloride  desired  does 


ALIPHATIC   SERIES  143 

not  lie  far  from  that  of  phosphorus  oxychloride  (iio°),thus  rendering 
a  fractional  distillation  for  the  separation  of  the  products  difficult,  the 
trichloride  is  always  used.  If  an  acid  does  not  react  too  energetically, 
as  is  the  case  with  the  higher  members  of  the  acetic  acid  series  with 
the  pentachloride,  this  is  used.  With  the  aromatic  acids,  the  latter  is 
used  exclusively,  since  the  trichloride  and  oxychloride  react  with  great 
difficulty : 

C7H15 .  CO .  OH  +  PC15  =  C7H15 .  CO .  Cl  +  POC13  +  HC1 

Caprylic  acid 

C6H5 .  CO .  OH  +  PC15  =  C6H5 .  CO .  Cl  +  POC13  +  HC1 

Bcnzoic  acid  Benzoyl  chloride 

Attention  is  called  to  the  fact  that  for  one  molecule  of  phosphorus 
pentachloride,  but  one  molecule  of  the  acid-chloride  is  obtained. 

The  phosphorus  oxychloride  is  used  generally  only  when  dealing 
with  the  salts  of  carbonic  acids,  upon  which  it  acts  as  indicated  by  the 
equation  : 

2  CH3 .  CO  .  ONa  +  POC13  -  2  CH3 .  CO  .  Cl  +  NaPO3  +  NaCl 

This  reaction  may  be  used  with  advantage  in  order  to  utilise  more 
of  chlorine  of  the  phosphorus  pentachloride  than  is  the  case  when  the 
latter  acts  upon  the  free  acids.  If  the  pentachloride  is  allowed  to  act 
on  a  sodium  salt,  as  above,  there  is  formed,  for  an  instant,  phosphorus 
oxychloride,  and  while  this  no  longer  acts  upon  the  free  acid,  it  can 
convert  two  other  molecules  of  the  salt  into  the  chloride : 

3  CH3 .  CO  .  ONa  +  PC15  =  3  CH3  .  CO .  Cl  +  NaPO3  +  2  NaCl 

In  this  way,  with  the  use  of  one  molecule  of  phosphorus  pentachloride, 
three  molecules  of  the  acid-chloride  are  obtained. 

The  lower  members  of  the  series  of  acid-chlorides  are  colourless 
liquids  ;  the  higher,  colourless  crystalline  substances.  They  boil,  gen- 
erally, at  ordinary  pressure  without  decomposition,  but  the  higher 
members  are  more  conveniently  distilled  in  a  vacuum.  The  boiling- 
points  of  the  acid-chlorides  are  lower  than  those  of  the  acids;  the 
replacement  of  hydroxyl  by  chlorine  usually  causes  a  lowering  of  the 
boiling-point. 


CH3 .  CO .  Cl    Boiling-point      5 1 c 
CH..CO.OH  "  118° 


C6H5.CO.C1    Boiling-point  199° 
C6H,.CO.OH  "  250° 


The  acid-chlorides  possess  pungent  odours.    They  fume  in  the  air,  since 
they  unite  with  the  moisture  and  decompose,  thus  forming  the  corre- 


144 


SPECIAL   PART 


spending  acid  and  hydrochloric  acid.  They  are  heavier  than  water, 
and  do  not  mix  with  it,  but  are  easily  soluble  in  indifferent  organic 
solvents  like  ether,  carbon  disulphide,  benzene. 

To  separate  the  chlorides  from  the  by-products  formed  by  the  phos- 
phorus chloride,  one  can  proceed  as  in  the  case  of  acetyl  chloride,  by 
distilling  off  the  volatile  chloride  from  the  non-volatile  phosphorus  acid, 
either  on  a  water-bath  or  over  a  free  flame.  In  order  to  separate  a 
chloride,  in  case  it  distils  without  decomposition,  from  the  volatile  phos- 
phorus oxychloride  formed  when  phosphorus  pentachloride  is  used,  a 
fractional  distillation  is  made.  In  other  cases,  the  mixture  is  heated 
in  a  vacuum  apparatus  on  an  actively  boiling  water-bath,  upon  which 
the  phosphorus  oxychloride  passes  over.  The  non-volatile  residue 
can  be  used,  in  many  cases,  without  further  purification;  it  may  be 
obtained  perfectly  pure  by  distilling  it  in  a  vacuum. 

Chemical  Reactions.  —  The  acid-chlorides  are  decomposed  by  water 
with  the  formation  of  the  corresponding  acid  and  hydrochloric  acid. 

CH3  .  CO  .  Cl  +  H2O  =  CH,  .  CO . OH  +  HC1 

This  decomposition  takes  place  often  with  extreme  ease  ;  the  chlorine 
atom  is  united  to  the  acid  radical  much  less  firmly  than  it  is  in  the  case 
of  an  alkyl  radical.  While  it  is  generally  necessary,  in  order  to  convert 
a  halogen  alkyl  into  an  alcohol,  to  boil  it  a  long  time  with  water,  often 
with  the  addition  of  sodium  hydroxide,  or  potassium  hydroxide,  a  car- 
bonate or  acetate,  the  analogous  transformation  of  an  acid-chloride 
takes  place  with  far  greater  ease.  With  the  lower  members,  e.g.  acetyl 
chloride,  the  reaction  begins  almost  instantly  at  the  ordinary  tempera- 
ture,, and  continues  with  violent  energy ;  but  it  is  necessary  to  heat  the 
higher  members  to  induce  the  transformation,  e.g.  benzoyl  chloride, 
which  will  be  prepared  later. 

EXPERIMENT  :  To  5  c.c.  of  water  in  a  test-tube  is  gradually 
added  -J-  c.c.  of  acetyl  chloride.  If  the  water  is  very  cold,  the 
oily  drops,  sinking  to  the  bottom,  do  not  mix  with  it,  and  may  be 
observed  for  a  short  time.  On  shaking  the  tube,  an  energetic 
reaction  sets  in  with  evolution  of  heat,  and  the  chloride  passes 
into  solution,  which  happens  immediately  if  the  water  is  not 
cold. 

The  acid-chlorides  react  with  alcohols  and  phenols  to  form  esters ; 


ALIPHATIC  SERIES  145 

CH3  .  CO  .  Cl  +  C2H5  .  OH  =  CH3  .  CO  .  OC2H5  +  HC1 

Ethyl  acetate 

CH3  .  CO  .  Cl  +  C6H5  .  OH  =  CH3  .  CO  .  OC6H5  +  HC1 

Phenol  Phenyl  acetate 

EXPERIMENT  :  To  i  c.c.  of  alcohol  in  a  test-tube,  cooled  with 
water,  add  an  equal  volume  of  acetyl  chloride,  drop  by  drop  ; 
this  mixture  is  then  treated  with  an  equal  volume  of  water,  the 
tube  being  cooled  as  before  ;  the  liquid  is  then  carefully  made 
weakly  alkaline  with  sodium  hydroxide.  If  the  pleasant-smelling 
ethyl  acetate  does  not  separate  out  on  the  water  solution  in  a 
mobile  layer,  finely  pulverised  salt  is  added  until  no  more  will 
dissolve.  This  will  cause  the  ethyl  acetate  to  separate  out. 

The  acid-chlorides  are  also  used  to  determine  whether  a  substance 
under  examination  contains  an  alcoholic  or  a  phenol  hydroxyl  group  or 
not.  If  the  compound  reacts  readily  with  an  acid-chloride,  it  contains 
either  alcoholic  or  phenol  hydroxyl,  since  compounds  containing  oxygen 
in  some  other  form  of  combination,  e.g.  as  in  ethers,  do  not  react  with 
acid-chlorides. 

The  addition  of  anhydrous  sodium  acetate  often  materially  assists  the 
reaction. 

Finally,  the  action  of  the  acid-chlorides  upon  alcohols  and  phenols 
is  made  use  of  to  separate  the  latter  from  solution,  or  in  order  to  detect 
them.  However,  benzoyl  chloride  is  most  generally  used  for  this  pur- 
pose, concerning  the  importance  of  which  more  will  be  said  later. 

Acid-chlorides  act  upon  the  salts  of  carbonic  acids,  forming  anhy- 
drides : 


=  CH3.CO.O.CO.CH3 

Acetic  anhydride 

The  next  preparation  will  deal  with  this  reaction.  The  acid-chlorides 
react  with  ammonia  as  well  as  with  primary  and  secondary  organic 
bases  with  great  ease  : 


CH3 .  CO .  Cl  4-  NH3  =  CH3 .  CO .  NH2  +  HC1, 

Acetamide 

CH3 . CO  .  Cl  4-  C6H5 .  NH2  =  C6H, .  NH  .  CO .  CH3  +  HC1 

Aniline        Acetanilide 


EXPERIMENT  :  To  i  c.c.  of  aniline,  acetyl  chloride  is  added  in 
drops  ;    an  energetic  reaction  takes  place  with  a  hissing  sound, 
L 


I46  SPECIAL  PART 

which  ceases  when  about  the  same  volume  of  the  chloride  is  added. 
The  mixture  is  cooled  with  water,  and  five  times  its  volume  of 
water  is  added,  upon  which  an  abundant  precipitate  of  acetanilide 
separates  out,  the  quantity  of  which  is  increased  by  rubbing  the 
walls  of  the  test-tube  with  a  glass  rod.  The  precipitate  is  filtered 
off,  and  recrystallised  from  hot  water.  Melting-point,  115°. 

This  reaction  is  also  used  to  characterise  organic  bases  by  converting 
them  into  their  best  crystallised  acid  derivatives,  and  in  order  to  detect 
small  quantities,  especially  of  liquid  bases,  by  a  melting-point  deter- 
mination. Since  the  tertiary  bases  do  not  react  with  acid-chlorides, 
because  they  no  longer  contain  any  ammonia  hydrogen,  this  reaction 
may  be  employed  to  decide  whether  a  given  base  is,  on  the  one  hand, 
primary  or  secondary,  or,  on  the  other,  tertiary. 

The  fact  that  hydrogen  in  combination  with  carbon  can  be  replaced 
by  an  acid  radical  by  the  use  of  an  acid-chloride  is  of  special  importance. 
In  this  connection,  the  Friedel-Crafts  ketone  synthesis  is  particularly 
mentioned.  This  will  be  taken  up  later,  in  practice.  The  reaction  is 
indicated  by  the  following  equation  : 

C6H6  +  CH3 .  CO .  Cl  -  C6H5 .  CO .  CH3  +  HCi 

Benzene  Acetophenone 

(in  presence  of  A1C13) 

The  acid-chlorides  are  also  of  service  for  the  synthesis  of  tertiary 
alcohols  (Butlerow's  Synthesis),  as  well  as  for  that  of  ketones.  The 
final  reactions  will  only  be  indicated  here;  in  regard  to  the  details, 
reference  must  be  made  to  larger  works. 

yen.    /CHS 

NCH, 

Zinc  methyl 


CH3 .  CO .  C1  +  Zn  =  CH3 .  C-CH  +  ZnO 

\CH3 


™ 


\  ^A13 

XOH 

Trimethyl  carbinol 


/CH3 

2  CH3 .  CO .  Cl  +  Zn<"          =2  CH3 .  CO .  CH3  +  ZnCl2 
\CHo 


Acetone 


ALIPHATIC  SERIES  147 


3.   REACTION:   PREPARATION   OF  AN  ANHYDRIDE  FROM  THE  ACID- 
CHLORIDE  AND  THE   SODIUM  SALT  OF  THE   ACID 

EXAMPLE  :    Acetic  Anhydride  from  Acetyl  Chloride 
and  Sodium  Acetate1 

For  the  preparation  of  acetic  anhydride  an  apparatus  similar 
to  that  used  in  the  preparation  of  acetyl  chloride  is  employed, 
except  that  the  fractionating  flask  is  replaced  by  a  tubulated  retort 
(Fig.  65,  page  I48).2 

To  70  grammes  of  finely  pulverised,  anhydrous  sodium  acetate 
(for  the  preparation  of  this,  see  below)  contained  in  the  retort, 
50  grammes  of  acetyl  chloride  are  added  drop  by  drop  from  a 
separating  funnel.  As  soon  as  the  first  half  of  the  chloride  is 
added,  the  reaction  is  interrupted  for  a  short  time,  in  order  that 
the  pasty  mass  may  be  stirred  up  with  a  glass  rod.  The  second 
half  is  then  allowed  to  run  in.  If  in  consequence  of  a  too  rapid 
addition  of  acetyl  chloride  some  of  it  should  distil  over  into  the 
receiver  undecomposed,  this  is  poured  back  into  the  funnel  and 
again  allowed  to  act  on  the  sodium  acetate.  The  separating 
funnel  is  then  removed,  the  tubulure  closed  with  a  cork,  and  the 
anhydride  distilled  off  from  the  salt  residue  by  means  of  a  luminous 
flame  which  is  kept  in  constant  motion.  The  distillate  is  finally 
purified  by  distilling  in  an  apparatus  similar  to  the  one  used  in  the 
rectification  of  the  acetyl  chloride  (see  also  Fig.  17)  with  the 
addition  of  3  grammes  of  finely  pulverised  anhydrous  sodium 
acetate,  which  serves  to  convert  the  last  portions  of  acetyl  chloride 
into  the  anhydride.  Boiling-point  of  acetic  anhydride,  138°. 
Yield,  about  50  grammes. 

Preparation  of  Anhydrous  Sodium  Acetate :  Crystallised  sodium 
acetate  contains  three  molecules  of  water  of  crystallisation.  In 
order  to  dehydrate  it  is  placed  in  a  shallow  iron  or  nickel  dish  and 
heated  over  a  free  flame  (120  grammes  for  this  experiment).  The 
salt  first  melts  in  the  water  of  crystallisation,  on  further  heating 
steam  is  copiously  evolved,  and  the  mass  solidifies  as  soon  as 

1  A.  87, 149. 

2  An  upright  coil  condenser  may  be  used,  in  which  case  an  adapter  is  unnecessary. 


148 


SPECIAL   PART 


the  main  portion  of  the  water  has  been  driven  off,  provided  the 
flame  is  not  too  large.  In  order  to  remove  the  last  portions  of  the 
water,  the  mass  is  now  heated  with  a  large  flame,  the  burner  being 
constantly  moved,  until  the  solidified  mass  melts  for  the  second  time. 
Care  must  be  taken  not  to  overheat ;  in  case  this  should  happen, 


FIG.  65. 

the  fact  will  be  recognised  by  the  evolution  of  combustible  gases  and 
the  charring  of  the  substance.  After  cooling,  the  salt  is  removed 
from  the  dish  with  a  knife.  If  commercial  anhydrous  sodium 
acetate  is  at  hand,  it  is  recommended  that  this  also  be  melted  once, 
since  when  it  is  kept  for  a  long  time  it  always  takes  up  water. 

The  reaction  of  acetyl  chloride  with  sodium  acetate  takes  place  in 
accordance  with  the  following  equation  : 

CH,CO\ 

CH3 .  CO  .  Cl  +  CHo .  CO  .  ONa  =  >O  +  NaCl 

CH3C(X 

This  reaction  is  capable  of  general  application,  and  the  anhydride  of 
the  acid  may  be  made  by  treating  its  chloride  with  the  corresponding 
sodium  salt.  The  so  called  mixed  anhydrides,  containing  two  different 


ALIPHATIC  SERIES  149 

acid  radicals,  can  also  be  prepared  by  this  reaction,  by  using  the  chloride 
and  sodium  salt  of  two  different  acids  : 

CH3.CO\ 

CH,.CO.Cl  +  CH3.CH2.CO.ONa  =  >O  +NaCl 

CH3.CH2.CO/ 

Since,  as  stated,  an  acid-chloride  may  be  obtained  from  an  alkali  salt  of 
the  acid  and  phosphorus  oxychloride,  it  is  not  necessary  for  the  prepa- 
ration of  an  anhydride  to  first  isolate  the  chloride ;  it  is  better  to  allow 
the  same  to  act  directly  on  an  excess  of  the  salt,  so  that  from  the  oxy- 
chloride and  salt  an  anhydride  is  directly  obtained : 

2  CH3 .  CO .  ONa  +  POC13  =  2  CH3 .  CO .  Cl  +  PO3Na  +  NaCl 

CH3.CO\ 
2CH3.CO.ONa  +  2CH3.CO.C1  =  2  >O  +  2  NaCl 

(~>T_]         CT\/ 

CHg.CO/ ^ 

CH3.CO\ 

4  CH3 .  CO .  ONa  +  POC13  =  2  >O  +  PO3Na  +  3  NaCl 

CH3.CO/ 

The  lower  members  of  the  acid-anhydride  series  are  colourless  liquids ; 
the  higher  members,  crystallisable  solids.  They  possess  a  sharp  odour, 
are  insoluble  in  water,  but  soluble  in  indifferent  organic  solvents.  Their 
specific  gravities  are  greater  than  that  of  water.  The  boiling-points 
are  higher  than  those  of  the  corresponding  acids : 

Acetic  acid.  118°, 
Acetic  anhydride,  138°. 

The  lower  members  can  be  distilled  without  decomposition  at  ordinary 
pressure  ;  but  the  higher  members  must  be  distilled  in  a  vacuum. 

The  chemical  conduct  of  anhydrides  toward  water,  alcohols,  and 
phenols,  as  well  as  bases,  is  wholly  analogous  to  that  of  the  chlorides ; 
but  the  anhydrides  react  with  more  difficulty  than  the  chlorides.  Thus 
with  water,  the  anhydrides  yield  the  corresponding  acids : 

CH3.CO\ 

>O  +  H9O  =  2CH3.CO.OH 
CH3.CO/ 

EXPERIMENT  :  5  c.c.  of  water  are  treated  with  ^  c.c.  of  acetic 
anhydride.  The  latter  sinks  to  the  bottom  and  does  not  dissolve 
even  on  long  shaking.  It  will  be  recalled  that  the  corresponding 
chloride  reacts  instantly  with  water  very  energetically.  If  the 
mixture  be  warmed,  solution  takes  place. 


150  SPECIAL   PART 

In  the  presence  of  alkalies,  solution  takes  place  much  more  readily 
with  the  formation  of  the  alkali  salts  : 


CH3.CO 
CH3 


.CO\ 

>0  +  2  NaOH  =  2CH3.CO.ONa  +  H2O 
.CO/ 


EXPERIMENT  :  Mix  5  c.c.  of  water  with  -|  c.c.  of  acetic  anhy- 
dride, and  add  a  little  caustic  soda  solution.  On  shaking,  without 
warming,  solution  takes  place. 

Anhydrides  of  high  molecular  weight  react  with  water  with  still 
greater  difficulty,  and  require  a  longer  heating  to  convert  them  into  the 
corresponding  acid. 

With  alcohols  and  phenols,  the  anhydrides  form  acid-esters  on  heat- 
ing, while  the  acid-chlorides  react  at  the  ordinary  temperature  : 

CHg.COv 

V)  +  C2H5.OH  =  CH3.CO.OC9H5  +  CH3.CO.OH 
CH3.CO/ 

CHo.CCK 

_>0  +  C6H5.OH  =  CH3.CO.OC6H5  +  CH3.CO.OH 

CH3  .  CO/  Phenyl  acetate 

It  is  to  be  noted  that  one  of  the  two  acid  radicals  in  the  anhydride  is 
not  available  for  the  purpose  of  introducing  the  acetyl  group  into  other 
compounds,  —  acetylating,  —  since  it  passes  over  into  the  acid. 

EXPERIMENT  :  2  c.c.  of  alcohol  are  added  to  i  c.c.  of  acetic  anhy- 
dride in  a  test-tube,  and  heated  gently  for  several  minutes.  It  is 
then  treated  with  water  and  carefully  made  slightly  alkaline.  The 
acetic  ester  can  be  recognised  by  its  characteristic  pleasant  odour. 
If  it  does  not  separate  from  the  liquid,  it  may  be  treated  with 
common  salt,  as  in  the  experiment  on  page  145. 

With  ammonia  and  primary  or  secondary  organic  bases,  the  anhy- 
drides react  like  the  chlorides  : 

CH3.COv 

NH3  +  >0  =  CH3.CO.NH2  +  CH3.CO.OH 

CH8.CO/ 

CH8.COv 
C6H5.NH2  +  ^O  =  C6H5.NH.CO.CH3  +  CH3.CO.OH 

CHo.    CO/ 


ALIPHATIC   SERIES  151 

EXPERIMENT  :  Add  i  c.c.  of  aniline  to  i  c.c.  of  acetic  anhydride, 
heat  to  incipient  ebullition,  and  then,  after  cooling,  add  twice  the 
volume  of  water.  The  crystals  of  acetanilide  separate  out  easily 
if  the  walls  of  the  vessel  be  rubbed  with  a  glass  rod ;  these  are 
filtered  off,  and  may  be  recrystallised  from  a  little  hot  water. 

The  acid-anhydrides  can,  therefore,  be  used,  like  the  chlorides,  for 
the  recognition,  separation,  characterisation,  and  detection  of  alcohols, 
phenols,  and  amines. 

In  order  to  complete  the  enumeration  of  the  reactions  of  the  acid- 
anhydrides,  it  may  be  mentioned  briefly  that  they  yield  alcohols,  and 
the  intermediate  aldehydes  when  treated  with  sodium  amalgam : 

CH3.CO\ 

>0  +  H2  =  CH3.CHO  +  CH3.CO.OH 

CHg.CO/  Aldehyde 

CH3 .  CHO      +  H2  =  CH3 .  CH2 .  OH 

It  is,  therefore,  possible  to  pass  from  the  anhydride  of  an  acid  to  its 
aldehyde  or  alcohol. 


4.    REACTION:    PREPARATION  OF  AN  ACID-AMIDE  FROM  THE 
AMMONIUM  SALT  OF  THE  ACID 

EXAMPLE  :   Acetamide  from  Ammonium  Acetate 1 

To  75  grammes  of  glacial  acetic  acid  heated  to  40-50°  in  a 
porcelain  dish  on  a  water-bath,  finely  pulverised  ammonium  car- 
bonate is  added  (100  grammes  will  be  necessary)  until  a  test- 
portion  diluted  in  a  watch-glass  with  water  just  shows  an  alkaline 
reaction.  The  viscous  mass  is  warmed  on  an  actively  boiling 
water-bath  to  80-90°,  until  a  few  drops  of  it  diluted  with  water 
just  show  an  acid  reaction ;  it  is  then  poured  (without  the  use  of 
a  funnel-tube)  directly  into  two  wide  bomb-tubes  of  hard  glass, 
which  have  been  previously  warmed  in  a  flame.  A  single  Volhard 
tube  (see  page  68)  is  much  more  convenient.  After  the  por- 
tions of  substance  adhering  to  the  upper  end  of  the  tube  have 
been  removed  by  melting  down  carefully  with  a  flame,  the  last 
traces  are  removed  with  filter-paper,  the  tube  sealed  and  heated 

i  B.  15, 979. 


152 


SPECIAL  PART 


for  five  hours  in  a  bomb-furnace  at  2  20-230°.  *  The  liquid  re- 
action product  is  fractionated  under  the  hood  in  a  distilling-flask 
provided  with  a  condenser.  There  is  first  obtained  a  fraction 
boiling  between  100-130°,  consisting  essentially  of  acetic  acid  and 
water.  The  temperature  then  rises  rapidly  to  180°  (an  extension 
tube  is  substituted  for  the  condenser,  see  page  22),  at  which 
point  the  acetamide  begins  to  distil.  The  fraction  passing  over 
between  180-230°  is  collected  in  a  beaker,  cooled  by  ice  water 
at  the  end  of  the  distillation,  and  the  walls  are  rubbed  with  a 
sharp-edged  glass  rod ;  the  crystals  separating  out  are  pressed  on 
a  drying  plate  to  remove  the  liquid  impurities.  By  another  dis- 
tillation of  the  pressed-out  crystals,  the  almost  pure  acetamide 
boiling  at  223°  passes  over.  Yield,  about  40  grammes.  The 
product  thus  obtained  possesses  an  odour  very  characteristic  of 
mouse  excrement ;  this  is  not  the  odour  of  pure  acetamide,  but 
of  an  impurity  accompanying  it.  In  order  to  remove  the  im- 
purity, a  portion  of  the  distilled  amide  is  again  pressed  out  on  a 
drying  plate,  and  then  crystallised  from  ether.  There  are  thus 
obtained  colourless,  odourless  crystals,  melting  at  82°. 

The  reaction  involved  in  the  preparation  of  an  amide  from  the  am- 
monium salt  of  the  acid  is  capable  of  general  application.  The  latter 
is  subjected  to  dry  distillation,  or  more  conveniently,  heated  in  a  sealed 
tube  at  220-230°  for  five  hours  : 

CH3 .  CO .  ONH4  =  CH, .  CO .  NH2  +  H2O 

In  order  to  purify  the  amide  thus  obtained,  the  reaction-mixture  may  be 
fractionated,  as  in  the  case  of  acetamide,  or  if  the  amide  separates  out 
in  a  solid  condition,  it  may  be  purified  by  filtering  off  the  impurities  and 
crystallising.  Substituted  acid-amides,  and  especially  easily  substituted 
aromatic  amides,  e.g.  acetanilide,  can  also  be  readily  obtained  by  this 
method,  by  heating  a  mixture  of  the  acid  and  amine  a  long  time  in  an 
open  vessel : 

CH3 .  COOH3N  .  C6H5  =  CH3 .  CO .  NH  .  C6H5  +  H2O 

Aniline  acetate  Acetanilide 

The  ammonium  salts  of  di-  and  poly-basic  acids  react  in  a  similar  way, 

*•&•'  CO.ONH4     CO.NH2 

I  =1  +2H20 

CO.ONH4      CO.NH2 


Ammonium  oxalate          Oxamide 


1  Above  this  temperature  the  tube  is  liable  to  explode. 


ALIPHATIC  SERIES  153 

Concerning  further  methods  of  preparation,  it  may  be  stated  thai 
acid-chlorides  or  anhydrides  when  treated  with  ammonia,  primary  or 
secondary  bases  form  acid-amides  very  easily: 

CH3.CO.C1   +  NH3  =  CH3.CO.NH2 
CHg. 


X 
>0 


+  NH3  =  CH3.CO.NH8  +  CH8.CO.  OH 


The  acid-amides  may  be  furthermore  obtained  by  two  methods  oi 
general  application:  (i),  by  treating  an  ethereal  salt  with  ammonia, 
and  (2),  by  treating  a  nitrile  with  water: 


Acetic  acid,  Boiling-point,      118° 
Acetamide,  „  223° 


Ethyl  acetate 

CH,  .  CN  +  H20  =  CH3  .  CO  .  NH« 

Acetonitrile 

The  acid-amides  are,  with  the  exception  of  the  lowest  member, 
formamide,  H  .  CO  .  NH2  (a  liquid),  colourless,  crystallisable  compounds, 
the  lower  members  being  very  easily  soluble  in  water,  e.g.,  acetamide  ; 
the  solubility  decreases  with  the  increase  of  molecular  weight,  until 
finally  they  become  insoluble.  The  boiling-points  of  the  amides  are 
much  higher  than  those  of  the  acids  : 

Proprionicacid,  Boiling-point,  141  ° 
Proprionamide,  „  213° 

While  the  entrance  of  an  alkyl  residue  into  the  ammonia  molecule 
does  not  change  the  basic  character  of  the  compound,  as  will  be  dis- 
cussed more  fully  under  methylamine,  the  entrance  of  a  negative  acid 
radical  enfeebles  the  basic  properties  of  the  ammonia  residue,  so  that 
the  acid-amides  possess  only  a  very  slight  basic  character.  It  is  true  that 
a  salt  corresponding  to  ammonium  chloride  —  CH3.CO.NH2.HC1  — 
can  be  prepared  from  acetamide  by  the  action  of  hydrochloric  acid; 
but  this  shows  a  strong  acid  reaction,  is  unstable,  and  decomposes 
easily  into  its  components.  If  it  is  desired  to  assign  to  the  acid-amides 
a  definite  character,  they  must  be  regarded  as  acids  rather  than  bases. 
One  of  the  amido-hydrogen  atoms  possesses  acid  properties  in  that  it 
may  be  replaced  by  metals.  The  mercury  salts  of  the  acid-amides  may 
be  prepared  with  especial  ease,  by  boiling  the  solution  of  the  amide 
with  mercuric  oxide  : 

2CH3.CO.NH2  -r  HgO  =  (CH3.CO.NH)2Hg  +  H,O 


154  SPECIAL  PART 

EXPERIMENT:  Some  acetamide  is  dissolved  in  water,  treated 
with  a  little  yellow  mercuric  oxide,  and  warmed.  The  latter  goes 
into  solution,  and  the  salt  of  the  formula  given  above  is  formed. 

The  amido-hydrogen  atoms  can  also  be  replaced  by  the  negative 
chlorine  and  bromine  atoms,  as  well  as  by  the  positive  metallic  atoms. 
These  substitution  compounds  are  obtained  by  treating  the  amide  with 
chlorine  or  bromine,  in  the  presence  of  an  alkali : 

CH3 .  CO  .  NHC1  CH3  .  CO  .  NHBr  CH3 .  CO  .  NBr2 

Acetchloramide  Acetbromamide  Acetdibromamide 

The  monohalogen  substituted  amides  are  of  especial  interest,  since,  on 
being  warmed  with  alkalies,  they  yield  primary  alkylamines : 

CH3 .  CO  .  NHBr  +  H2O  =  CH3 .  NH2  +  HBr  +  CO2 

This  important  reaction  will  be  taken  up  later,  under  the  preparation 
of  methyl  amine  from  acetamide. 

In  the  acid-amides,  the  acid  radical  is  not  firmly  united  with  the 
ammonia  residue  ;  this  is  shown  by  the  fact  that  they  are  saponified, 
i.e.  decomposed  into  the  acid  and  ammonia,  on  boiling  with  water, 
more  rapidly  by  warming  with  alkalies : 

CH3 .  CO  .  NH2  +  H2O  =  CH, .  CO .  OH  +  NH3 

EXPERIMENT  :  Heat  some  acetamide  in  a  test-tube  with  caustic 
soda  solution.  A  strong  ammoniacal  odour  is  given  off,  while 
the  solution  contains  sodium  acetate. 

If  an  acid-amide  is  treated  with  a  dehydrating  agent,  e.g.,  phosphorus 
pentoxide,  it  is  converted  into  a  nitrile  : 

CH3 .  CO .  NH2  =  CH3 .  CN  +  H2O 

Acetonitrile 

The  same  result  is  obtained  by  treating  it  with  phosphorus  penta- 
chloride  ;  but  in  this  case  the  intermediate  products,  the  amide-chlorides 
or  imide-chlorides  are  formed  : 

CH3 .  CO  .  NH2  +  PC15  -  CH3 .  CC12 .  NH2  +  POCL 

Amide-chloride 

The  very  unstable  amide-chloride  then  passes  over,  with  the  loss  of  one 
molecule  of  hydrochloric  acid,  into  the  more  stable  imide-chloride  : 
CH, .  CC12 .  NH2  =  CH3.  CC1=  NH  4-  HC1 

Imide-chloride 

And  this  finally  into  the  nitrile, 

CH3.CC1=NH  =  CH3.CN  +  Hd 


ALIPHATIC  SERIES  155 


5.  REACTION:    PREPARATION  OP  AN  ACID-NITRILE  FROM  AN 
ACID- AMIDE 

EXAMPLE  :  Acetonitrile  from  Acetamide 1 

To  15  grammes  of  phosphoric  anhydride,  contained  in  a  small, 
dry  flask,  10  grammes  of  dry  acetamide  are  added.  After  the  two 
substances  are  shaken  well  together,  the  flask  is  connected  with  a 
short  condenser,  and  then  heated  carefully,  with  a  not  too  large 
luminous  flame  kept  in  constant  motion.  The  reaction  proceeds 
with  much  foaming.  After  the  mixture  has  been  heated  a  few 
minutes,  the  acetonitrile  is  then  distilled  over  with  a  large  luminous 
flame,  kept  in  constant  motion,  into  the  receiver  (test-tube).  The 
distillate  is  treated  with  half  its  volume  of  water,  and  then  solid 
potash  is  added  until  it  is  no  longer  dissolved  by  the  lower  layer 
of  liquid.  The  upper  layer  is  removed  with  a  capillary  pipette 
and  distilled,  a  small  amount  of  phosphoric  anhydride  being  placed 
in  the  fractionating  flask  for  the  complete  dehydration  of  the  nitrile. 
Boiling-point,  82°.  Yield,  about  5  grammes. 

If  an  acid-amide  is  heated  with  a  dehydrating  agent  (phosphorus 
pentoxide,  pentasulphide,  or  pentachloride),  it  loses  water,  and  passes 
over  into  the  nitrile,  e.g. : 

CH3.CO  NH2  =  CH3.CEEN  + H2O 

Acetonitrile 

Since,  as  has  just  been  done,  the  acid-amide  may  be  made  by  dehy- 
drating the  ammonium  salt  of  an  acid,  thus,  in  a  single  operation  the 
nitrile  may  be  obtained  directly  from  the  ammonium  salt,  if  it  is  treated 
with  a  powerful  dehydrating  agent,  e.g.  ammonium  acetate  heated  with 
phosphoric  anhydride : 

CH3.COONH4=  CH3.CN  +  2H2O 

The  acid-nitriles  may  also  be  obtained  by  heating  alkyl  iodides  (or 
bromides,  chlorides)  with  alcoholic  potassium  cyanide : 

CH,|I  +  K|CN  =  CH3.  CN  +  KI 

CH2Br  CH9.CN 

|  +2KCN=I  +2KBr 

CH2Br  CH2.CN 

____________  Ethylene  cyanide 

1  A.  64, 33*- 


156  SPECIAL  PART 

C6H5 .  CH2 .  Cl  +  KCN  =  C6H5 .  CH2 .  CN  +  KC1 

Benzyl  chloride  Benzyl  cyanide 

or  by  the   dry  distillation   of  alkyl  alkali   sulphates  with   potassium 

cyanide :  

XO|C2H5      CNJK 
SO,/  ~~~fT~         =  C2H5 .  CN  +  K2SO4 


>K 

Ethyl  potassium  sulphate  Proprionitrile 

These  two  reactions  differ  from  those  above  in  that  the  introduction  of 
a  new  atom  of  carbon  is  brought  about.  The  nitriles  thus  appear  to  be 
cyanides  of  the  alkyls,  and,  therefore,  may  be  equally  well  designated 
as  cyanides,  e.g. : 

CH3 .  CN  =  Acetonitrile     =  Methyl  cyanide 
CgH^CN  =  Proprionitrile  =  Ethyl  cyanide 
etc.  etc.  etc. 

The  lower  members  of  the  nitrile  series  are  colourless  liquids,  the 
higher  members,  crystallisable  solids ;  the  solubility  in  water  decreases 
with  the  increase  in  molecular  weights.  If  they  are  heated  with  water 
up  to  1 80°  under  pressure,  they  take  up  one  molecule  of  water  and  are 
converted  into  the  acid-amides : 

CH3.CN  +  H20  =  CH3.CO.NH2 

On  heating  with  acids  or  alkalies,  they  take  up  two  molecules  of  water, 
and  pass  over  into  the  ammonium  salt  as  an  intermediate  product  : 

CH3.  CN  +  2  H2O  =  CH3 .  COONH4 

which  immediately  reacts  with  the  alkali  or  acid,  in  accordance  with 
the  following  equations : 

CH3.COONH4  +  KOH  =  CH3.COOK  +  NH3  +  H2O 
CH3.COONH4  +  HC1  =  CH3.COOH  +  NH4C1 

This  process  is  called  "  saponification." 

If  nascent  hydrogen  (e.g.  from  zinc  and  sulphuric  acid)  be  allowed 
to  act  on  nitriles,  primary  amines  are  formed  (Mendius1  reaction)  : l 

CH3.CN  +  2  H2  =  CH3.CH2.NH2 

Ethyl  amine 


l  A.  lai,  129. 


ALIPHATIC  SERIES  157 

Further,  but  of  less  importance,  general  reactions  may  be  indicated 
by  the  following  equations: 

CH3  .  CN  +  H2S  =  CH8  .  CS  .  NH2 

Thioacetamide 

CH3.CO\ 
CH3  .  CN  +  CH3  .  CO  .  OH  =  >NH  =  Diacetamide 

CH3.CO/ 
CH3.CO\ 

CH3  .  CN  +  >0  =  N(CO  .  CHo)3  =  Triacetamide 

CH3.CO/ 


NH2 


CH3.CN  +  NH2.OH       = 

Hydroxylamine  Acetamide-oxime 

CH3.CN 

Imide-chloride 

6.  REACTION:   PREPARATION  OF  AN  ACID-ESIER  FROM  THE  ACID 
AND  ALCOHOL 

EXAMPLE  :  Acetic  Ester  from  Acetic  Acid  and  Ethyl  Alcohol1 

A  i-litre  flask,  containing  a  mixture  of  50  c.c.  of  alcohol  and  50 
c.c.  of  concentrated  sulphuric  acid,  is  closed  by  a  two-hole  cork ; 
through  one  hole  passes  a  dropping  funnel,  through  the  other  a 
glass  delivery  tube  connected  with  a  long  condenser  or  coil  con- 
denser. The  mixture  is  heated  in  an  oil-bath  to  140°  (thermome- 
ter in  oil) ;  when  this  temperature  is  reached,  a  mixture  of  400  c.c. 
of  alcohol  and  400  c.c.  of  glacial  acetic  acid  is  gradually  added 
through  the  funnel,  at  the  same  rate  at  which  the  ethyl  acetate 
(acetic  ester),  formed  in  the  reaction,  distils  over.  In  order  to 
remove  the  acetic  acid  carried  over,  the  distillate  is  treated  in  an 
open  vessel  with  a  dilute  solution  of  sodium  carbonate  until  the 
upper  layer  will  not  redden  blue  litmus  paper.  The  layers  are 
now  separated  with  a  dropping  funnel ;  the  upper  layer  is  filtered 
through  a  dry  folded  filter,  and  shaken  up  with  a  solution  of  100 

i  Bl.  33,  350. 


158  SPECIAL   PART 

grammes  of  calcium  chloride  in  100  grammes  of  water,  in  order 
to  remove  the  alcohol.1  The  two  layers  are  again  separated  with 
the  funnel,  the  upper  one  dried  with  granular  calcium  chloride 
and  then  distilled  on  the  water-bath  (see  page  16).  Boiling 
point,  78°.  Yield,  about  80-90  %  of  the  theory. 

The  formation  of  an  ester  from  acid  and  alcohol  is  analogous  to  the 
formation  of  a  salt  from  an  acid  and  a  metallic  hydroxide  : 

NO3  .  H  +  Na  .  OH  =  NO3  .  Na  +  H2O 
CH3 .  COOH  +  C2H5OH  =  CH3  .  COOC,H5  +  H2O 

The  two  reactions  take  place  quantitatively,  but  not  in  a  similar 
manner.  A  strong  acid  reacts  almost  quantitatively  with  an  equivalent 
weight  of  a  strong  base,  and  the  product  of  this  neutralisation  is  a  salt. 
Upon  this  depend  the  processes  of  acidimetry  and  alkalimetry.  But 
equimolecular  quantities  of  an  acid  and  an  alcohol  do  not  yield  the 
theoretical  quantity  of  the  ester.  A  maximum  quantity  of  ester  is 
formed,  but  this  falls  short  of  the  quantity  required  by  theory,  and  it  is 
impossible,  even  when  the  reacting  substances  are  kept  in  contact,  to 
convert  the  unchanged  acid  and  alcohol  into  ester  beyond  a  certain 
limit.  If.  for  example,  equimolecular  quantities  of  acetic  acid  and 
alcohol  are  allowed  to  interact,  only  two-thirds  of  these  enter  into  the 
reaction,  the  maximum  yield  of  ester  being  66.7%  of  the  theory.  It  is 
impossible  to  cause  a  union  between  the  remaining  one-third  of  acetic 
acid  and  alcohol,  even  when  the  reaction  is  continued  for  a  long  time. 
The  difference  in  the  quantitative  course  of  the  reaction  in  the  forma- 
tion of  an  ester  is  due  to  the  "reversibility  of  the  reaction";  i.e.  the 
reaction  products  on  the  right-hand  side  of  the  equation  (ester  and 
water)  will  interact  in  such  a  manner  as  to  reverse  the  reaction : 

CH3 .  COOC2H5  +  H2O  =  CH3 .  COOH  +  C2H5OH 
In  reactions  of  this  order  the  two  sides  of  the  equation  are  united,  not 
by  an  equation  sign,  but,  as  proposed  by  van't  Hoff,  by  two  arrows 
pointing  in  opposite  directions  : 

CH3 .  COOH  +  C2H5OH  ^>  CH3  .  COOC2H5  +  H2O 
The  reaction  in  the  neutralisation  of  a  strong  acid  with  a  strong 
base  is,  on  the  other  hand,  unlike  esterification,  since  it  is  "  an  irre- 
versible or  a  complete  reaction  " ;  the  water  that  is  liberated  does  not 
react  with  the  salt  to  reverse  the  reaction  and  regenerate  the  acid  and 
the  base.  In  reality  this  difference  does  not  exist.  All  reactions  are 

1  Calcium  chloride  forms  a  compound  with  alcohol.     (Compare  page  54.) 


ALIPHATIC   SERIES  159 

reversible.  But  when  a  reaction  product  is  extremely  insoluble,  or 
when  it  is  a  gas,  or  when  for  other  reasons  the  final  products  have 
little  tendency  to  react  and  bring  about  the  reverse  change  (and  this 
is  the  case  in  the  above  example  of  the  neutralisation  of  a  strong  acid 
with  a  strong  base),  then  one  of  the  two  opposing  reactions  is  said  to 
be  complete  "  within  measurable  limits,"  and  it  is  called  an  u  irreversible 
reaction  in  the  ordinary  sense,"  although  not  in  the  strictest  sense.  — 
While  in  irreversible  reactions  chemical  equations  enable  us  to  calculate 
the  amount  of  the  products  from  given  quantities  of  reacting  substances, 
in  reversible  reactions  strictly  quantitative  stoichiometric  methods 
do  not  give  the  desired  information.  But  by  the  aid  of  the  highly 
important  Law  of  Mass  Action  (Guldberg  and  Waage,  1867),  it  is  pos- 
sible to  determine  to  what  extent  a  reversible  reaction  may  be  complete. 
As  has  already  been  mentioned,  when  equimolecular  quantities  of 
acetic  acid  and  ethyl  alcohol  are  allowed  to  react  for  some  time,  only 
two-thirds  of  these  substances  will  be  transformed  into  acetic  ester  and 
water.  A  "  state  of  equilibrium  "  will  finally  be  established,  and  the 
reaction  mixture  will  have  the  following  constant  composition  : 

|  ester  -f  f  water  +^  acetic  acid  +  i  alcohol 

The  same  equilibrium  is  established,  if,  instead  of  a  mixture  of  acid 
and  alcohol,  a  similar  mixture  of  ester  and  water  is  taken.  In  this  case 
the  ester  will  be  partially  saponified  into  acetic  acid  and  alcohol,  but 
the  reaction  will  proceed  only  until  £  of  the  ester  is  saponified.  An 
equilibrium  will  once  more  be  established  as  above,  so  that  f  of  ester 
and  water,  and  £  of  acetic  acid  and  alcohol  will  be  obtained. 

It  must  not  be  assumed  that  in  an  equilibrium  of  this  kind  the  mole- 
cules of  the  four  substances  remain  unaltered  (static  equilibrium).  On 
the  contrary,  while  acetic  acid  and  alcohol  are  forming  ester  and  water, 
the  molecules  of  ester  and  water  are  simultaneously  reacting  to  bring 
about  the  reverse  change  (dynamic  equilibrium).  In  spite  of  this  con- 
tinuous reaction  an  equilibrium  will  exist,  i.e.  the  composition  of  the 
system  will  remain  unaltered,  when  the  velocities  of  the  two  opposing 
reactions  are  the  same,  i.e.  when  in  unit  time  an  equal  number  of  ester 
molecules  is  formed  and  saponified. 

The  formation  of  ethyl  acetate  from  acetic  acid  and  alcohol  may  be 
expressed  by  the  following  equation  of  mass  action  : 


where  Cs,  CA,  CE,  Cw  show  the  "  concentration  "  of  acetic  acid,  alcohol, 
ester,  and  water  respectively,  and  K  is  a  constant.     By  concentration, 


160  SPECIAL   PART 

or  "  active  mass  "  (Guldberg  and  Waage)  is  not  meant  the  weight  of 
each  substance  in  the  total  volume  or  in  unit  volume,  but  the  relative 
number  of  molecules,  i.e.  the  weight  of  each  substance  divided  by  its 
molecular  weight  (the  number  of  gramme-molecules  or  moles).  The 
equation  shows  that  when  the  four  substances  are  in  equilibrium  with 
one  another,  the  product  of  the  concentrations  of  acetic  acid  and  alco- 
hol divided  by  the  product  of  the  concentrations  of  ester  and  water 
will  be  equal  to  a  constant.  How  can  this  constant  be  calculated  ? 
We  simply  ascertain  by  analytical  methods  the  weights  of  the  four 
substances  that  are  in  equilibrium  with  one  another  in  a  concrete  ex- 
ample, calculate  the  concentrations  in  accordance  with  deductions  men- 
tioned above,  and  introduce  these  values  into  the  equation  given. 
This  may  be  readily  done  in  our  example,  since  three  of  the  substances 
(alcohol,  ester,  and  water)  are  neutral,  and  the  quantity  of  the  fourth, 
the  acetic  acid,  may  be  easily  ascertained  by  titration.  If  we  take,  e.g., 
equimolecular  quantities  of  acetic  acid  and  alcohol,  namely,  60  grammes 
of  acetic  acid  and  46  grammes  of  alcohol  (and  this  will  contain  an 
equal  number  of  molecules),  we  can  determine  the  amount  of  acid  in 
one  c.c.  of  this  mixture,  at  the  first  minute,  by  titration.  If  we  now 
allow  the  two  substances  to  react  for  some  time,  and  titrate  one  c.c.  of 
the  mixture  at  stated  intervals,  the  titre  of  the  acid  will  be  found  to 
diminish  gradually,  until  finally  it  remains  constant,  due  to  equilibrium. 
If  now  we  compare  the  maximum  first  titre  with  the  final  minimum 
titre,  we  shall  find  that  the  latter  is  exactly  one-third  of  the  former ; 
i.e.  at  equilibrium  only  one-third  of  the  original  molecules  of  acetic 
acid  remain  uncombined,  the  other  two-thirds  having  been  changed 
into  the  ester.  Since  one  molecule  of  acid  yields  one  molecule  of  ester, 
the  number  of  ester  molecules  is  exactly  two-thirds  of  acetic  acid  mole- 
cules used  originally  for  the  experiment.  Since  further,  with  the 
formation  of  every  ester  molecule  a  water  molecule  is  also  formed,  the 
number  of  water  molecules  is  also  exactly  two-thirds  of  acetic  acid 
molecules  taken  originally.  And  finally,  since  with  every  molecule  of 
acid  one  molecule  of  alcohol  reacts  to  form  the  ester,  two-thirds  of  the 
alcohol  molecules  are  used  up,  and  only  one-third  remain  unchanged  at 
equilibrium.  We  have  thus  determined  the  amount  of  all  four  sub- 
stances at  equilibrium  by  a  mere  titration.  Consequently,  we  have  the 
following  values  in  our  equation  : 

Ca  =  1 1   CA  =  I ;   Cjt  =  | ;   Cw=§. 
If  we  carry  these  values  into  the  above  equation,  we  obtain : 

*-=iii=£ 

M      4 


ALIPHATIC   SERIES  l6l 

Thus  when  we  have  accurately  determined  the  value  of  A'  in  a  single 
experiment,  we  shall  be  in  a  position  to  calculate  the  quantitative  yield 
of  acetic  ester  at  equilibrium  for  all  proportions  of  acetic  acid  and 
alcohol.  Suppose  we  use,  e.g.,  one  gramme-molecule  of  acetic  acid  with 
two  gramme-molecules  of  alcohol,  and  let  x  be  the  number  of  gramme- 
molecules  of  ester  at  equilibrium  ;  the  gramme-molecular  quantity  of 
water  will  also  be  represented  by  x.  The  gramme-molecular  quantity 
of  unchanged  acetic  acid  will  then  be  (i  —  x),  and  that  of  unchanged 
alcohol  will  be  (2  —  x).  Making  these  substitutions  in  our  equation, 
we  obtain  : 

(i  -x).  (2  -x)  _  \ 
x.x  4 

X=  2  ±  2VJ 

Since  the  quantity  of  acetic  acid  used  is  only  one  gramme-molecule, 
x  cannot  be  greater  than  one,  and  we  are  thus  concerned  only  with  the 
negative  sign.  Thus  .ris  equal  to  2  —  2>/|  =  0.85,  i.e.  0.85  gramme- 
molecules  of  ester  are  obtained  at  equilibrium,  i.e.  85%  of  the  acetic 
acid  is  transformed  into  ester.  If,  therefore,  instead  of  using  equi- 
molecular  quantities  of  acetic  acid  and  alcohol,  we  double  the  theoreti- 
cal quantity  of  the  latter,  85  %  of  the  acetic  acid  will  be  transformed  into 
ester  instead  of  66.7  %. 

The  following  problems  may  be  solved  in  this  connection  : 
How  much  ester  will  be  formed  when  one  gramme-molecule  of  acetic 
acid  is  treated  with  three  gramme-molecules  of  alcohol  ?  How  much 
ester  will  be  formed  when  30  grammes  of  acetic  acid  and  50  grammes  of 
alcohol  are  used  ?  What  proportions  of  acetic  acid  and  alcohol  must 
be  used  in  order  to  transform  75  %  of  the  former  into  ester  ? 

As  the  above  example  shows,  the  yield  of  ester  from  the  same 
quantity  of  acetic  acid  is  greater,  the  larger  the  amount  of  alcohol  used. 
This  also  follows  directly  from  the  equation  of  mass  action  given  above. 
As  we  have  seen,  K  must  have  the  constant  value  of  \  for  all  propor- 
tions of  reacting  substances.  Thus  when  CA,  the  concentration  of 
the  alcohol,  is  increased,  the  remaining  three  quantities  will  also  be 
changed  in  such  a  manner  that  the  quotient  will  have  a  constant  value. 
This  can  only  happen  when  the  quantities  in  both  denominators  in- 
crease, i.e.  when  the  concentrations  of  the  ester  and  the  water  formed 
at  the  same  time  become  greater.  The  equalisation  of  the  quotient, 
however,  takes  place  not  only  through  the  denominator,  but  also  through 
the  numerator ;  because  when  more  ester  is  formed,  more  acetic  acid  will 
also  be  used  up.  This  is  shown  by  the  decrease  in  the  concentration 
of  acetic  acid.  Thus  a  large  excess  of  alcohol  is  taken  when  it  is  desired 


1 62  SPECIAL   PART 

to  convert  an  acid,  as  completely  as  possible,  into  an  ester.  If,  on  the 
other  hand,  it  is  desired  to  convert  an  alcohol  into  an  ester  quantita 
tively,  a  large  excess  of  acid  is  used. 

The  practical  application  of  these  principles  in  preparation  work  has 
already  been  pointed  out  under  ethyl  bromide. 

In  the  preparation  of  ethyl  acetate  described  above,  sulphuric  acid  is 
also  used  in  addition  to  acetic  acid  and  alcohol.  This  reacts  in  two 
ways.  It  is  a  well-known  fact  that  concentrated  sulphuric  acid  com- 
bines with  water  chemically.  Consequently,  the  water  liberated  during 
the  formation  of  ester  is  either  completely,  or  in  part,  removed,  and  the 
reverse  reaction  from  right  to  left,  i.e.  the  saponification  of  the  freshly 
formed  ester,  is  either  rendered  impossible  or  difficult.  Thus  the  yield 
of  ester  is  much  larger  in  the  presence  of  sulphuric  acid.  But  sulphuric 
acid  also  acts  as  a  catalytic  agent  in  the  reaction,  i,e.  it  accelerates  the 
formation  of  ester,  as  well  as  its  saponification,  and  indeed  in  the  same 
ratio,  so  that  the  state  of  equilibrium  is  not  changed.  Other  acids  may 
also  be  employed  as  catalytic  agents  in  this  sense.  Thus  esters  may 
be  formed  by  simply  conducting  hydrochloric  acid  gas  into  a  mixture 
of  acid  and  alcohol,  or  by  heating  the  acid  with  alcoholic  hydrochloric 
acid  (containing  a  small  percentage  of  HC1).  (Compare  B.  28,  3252.) 
The  speed  of  the  catalytic  action  is  proportional  to  the  strength  of  the 
acid  used  as  a  catalytic  agent.  The  stronger  the  dissociation  of  the 
acid,  i.e.  the  greater  the  concentration  of  hydrogen  ions  in  the  reaction 
mixture,  the  more  rapid  the  formation  of  the  ester.  By  this  method, 
and  others,  is  the  strength  of  many  acids  determined. 

In  many  cases,  where  the  salts  of  organic  acids  are  more  readily 
obtained  than  the  free  acids,  they  may  be  used  for  the  preparation  of 
the  esters  by  heating  them  directly  with  alcohol  and  sulphuric  acid. 
Other  methods  for  the  preparation  of  acid-esters  have  been  referred  to, 
and,  in  part,  carried  out  practically  on  the  small  scale  in  the  foregoing 
preparations,  so  that  at  this  point  it  is  only  necessary  to  recall  the 
equations : 

(1)  CH., .  CO  .  OAg  +  IC2H5  =  CH3  .  CO  .  OC2H5  +  Agl, 

(2)  CH3 .  CO  .  Cl  +  CaH5 .  OH  =  CH8  .  CO  .  OC2H5  +  HC1, 

CTT        (~*O\ 

(3)  CH3 '  co/  O  +  C2H5 .  OH  =  CH3 .  CO  .  OC2H5  +  CH3 .  CO  .OH. 

(4)  Acid-esters  may  also  be  readily  obtained  by  treating  the  alkali 
salts  of  acids  with  alkyl  sulphate,1  at  the  ordinary  temperature  : 

R .  CO .  OMe  +  (CH3)2SO4  =  R  .  CO  .  OCH,  +  CH3 .  SO4 .  Me 
(Compare  B.  37,  3658.)     It  must  be  remembered  that  methyl  sulphate 
is  poisonous. 

1  The  hydrogen  atom  in  a  hydroxyl  group  in  phenols,  as  well  as  a  hydrogen 
atom  in  combination  with  nitrogen,  may  readily  be  exchanged  for  a  methyl  group 
by  the  use  of  dimethyl  sulphate.  See  A.  327,  104. 


ALIPHATIC   SERIES  163 

Concerning  the  purification  of  the  acid-esters,  it  may  be  mentioned, 
that  the  crude  reaction-product  is  shaken  with  a  sodium  carbonate 
solution  until  the  ester  no  longer  shows  an  acid  reaction.  The 
alcohol  may  be  removed  from  esters  difficultly  soluble  in  water  by 
repeatedly  washing  with  water ;  in  case  an  ester  is  moderately  soluble 
in  water,  as  ethyl  acetate,  it  is  better  to  use  a  solution  of  calcium 
chloride. 

The  lower  members  of  the  series  of  acid-esters  are  colourless  liquids 
with  pleasant,  fruit-like  odours ;  the  higher  members,  as  well  as  those 
of  the  aromatic  acids,  are  crystallisable  compounds.  The  boiling-points 
of  esters  containing  alky!  residues  of  small  molecular  weights  (CH3, 
C2H5,  C3H7)  are  lower  than  those  of  the  corresponding  acids ;  the 
entrance  of  more  complex  alkyl  residues  raises  the  boiling-points : 

CH3 .  CO .  OCH3  Boiling-point,  57° 

CH3.CO.OC2H5  «           «  78° 

CH3.CO.OH    '  "           «  118° 

CH3.CO.OC6H13  «           «  169° 

Hexyl  acetate 

As  already  mentioned,  the  esters  are  saponified  by  heating  with  water : 

CH3 .  CO .  OC2H5  +  H20  =  CH3 .  CO .  OH  +  C2H5 .  OH 
The  saponification  is  effected  more  readily  by  heating  with  alkalies  : 
CH3 .  CO .  OC2H5  +  KOH  =  CH3 .  CO .  OK  +  C2H5 .  OH 

Other  methods  of  saponification  will  be  fuither  discussed  when  a 
practical  example  is  taken  up.  The  action  of  ammonia  upon  acid- 
esters,  forming  acid-amides,  has  already  been  referred  to  under  acet- 
amide : 

CH3 .  CO .  OC2HS  +  NH3  =  CH3 .  CO .  NH2  +  C2H5 .  OH. 

7.  REACTION:  SUBSTITUTION  OP  HYDROGEN  BY  CHLORINE 
EXAMPLE  :  Monochloracetic  Acid  from  Acetic  Acid  and  Chlorine  l 

A  current  of  dry  chlorine  is  passed  into  a  mixture  of  150 
grammes  of  glacial  acetic  acid  and  1 2  grammes  of  red  phosphorus, 
contained  in  a  flask  provided  with  a  delivery  tube  and  an  inverted 

iR.  23,222;  A.  102,1. 


1 64  SPECIAL   PART 

condenser;  the  flask  is  heated  on  a  rapidly  boiling  water-bath, 
and  must  be  placed  in  such  a  position  as  to  receive  as  much  light 
as  possible.  The  best  result  is  obtained  by  performing  the  reac- 
tion in  the  direct  sunlight,  since  the  success  of  the  chlorination 
depends  essentially  on  the  action  of  the  sun's  rays.  The  reaction 
is  ended  when  a  small  test- portion  cooled  with  ice-water  solidifies 
on  rubbing  the  walls  of  the  vessel  (test-tube)  with  a  glass  rod. 
In  summer  the  chlorination  may  require  a  single  day,  while  dur- 
ing the  cloudy  days  of  winter,  two  days  may  be  necessary.  For 
the  separation  of  the  monochloracetic  acid  the  reaction-product  is 
fractionated  from  a  distilling  flask  connected  with  a  long  air  con- 
denser. The  fraction  passing  over  from  150-200°  is  collected  in 
a  separate  beaker ;  this  is  cooled  in  ice-water  and  the  walls  rubbed 
with  a  glass  rod.  The  portion  solidifying,  consisting  of  pure  mono- 
chloracetic acid  is  rapidly  filtered  with  suction,  the  loose  crystals 
being  pressed  together  with  a  spatula  or  mortar-pestle.  The  suc- 
tion must  not  be  continued  too  long,  because  the  monochloracetic 
acid  gradually  becomes  liquid  in  warm  air.  The  filtrate  is  again 
distilled,  and  the  portion  passing  over  between  1 70-200°  is  col- 
lected in  a  separate  vessel.  This  is  treated  as  before  (cooling 
and  filtering),  and  there  is  obtained  a  second  portion  of  mono- 
chloracetic acid ;  this  is  united  with  the  main  quantity,  which  is 
again  distilled.  The  product  thus  obtained  is  perfectly  pure. 
Boiling-point,  186°.  Yield  varying,  80-125  grammes. 

Since  monochloracetic  acid,  especially  when  warm,  attacks  the 
skin  with  great  violence,  care  must  be  taken  in  handling  it. 

Chlorine  or  bromine  substitution  products  of  aliphatic  carbonic  acids 
can  be  obtained  by  the  direct  action  of  the  halogen  on  the  acids : 

CH3.CO.OH  +  C12  =  CHUC1.CO.OH  +  HC1 
(Br2)          (Br)  (HBr) 

If  the  reaction  is  allowed  to  continue  for  a  long  time,  other  substitution 
products  can  also  be  obtained.  But  the  action  of  chlorine  or  bromine 
on  acids  is  very  sluggish.  It  may  be  substantially  facilitated  by  certain 
conditions.  If,  e.g.,  the  operation  is  conducted  in  direct  sunlight,  the 
reaction  proceeds  much  more  rapidly  than  in  a  dark  place.  The  reac- 
tion is  assisted  more  effectively  by  adding  a  so-called  "  carrier."  Iodine 


ALIPHATIC  SERIES  165 

may  be  used  as  such  for  the  introduction  of  chlorine  or  bromine.  When 
added  in  small  quantities  to  the  substance  to  be  substituted,  it  causes 
the  substitution  to  take  place  more  rapidly  and  completely.  The  con- 
tinuous action  of  this  carrier  depends  upon  the  following  facts  :  In 
the  first  phase  of  the  reaction,  chlorine  iodide  is  formed  : 

(i)  Cl  +  I  =  IC1 

This  acts,  then,  as  a  chlorinating  agent  in  the  second  phase,  according 
to  the  following  reaction  : 

(2)  CH3  .  CO  .  OH  +  IC1  =  CH2C1  .  CO  .  OH  4-  HI 
The  chlorine  acts  upon  the  hydriodic  acid  as  follows  : 
(3)  HI  +  C13  =  IC1  +  HC1 

The  molecule  of  chlorine  iodide  is  thus  formed  anew  (equation  i) 
and  can  chlorinate  another  molecule  of  acetic  acid,  and  so  on.  The 
action  of  the  iodine  in  the  last  case  depends  upon  the  fact  that  the 
molecule  of  chlorine  iodide  (1C1)  is  more  easily  decomposed  into  its 
atoms  than  the  molecule  of  chlorine  (C12)  .  The  disadvantage  neces- 
sarily incident  to  the  use  of  iodine  as  a  carrier  is,  that  the  reaction- 
product  is  easily  contaminated  with  iodine  derivatives,  —  in  small 
quantities,  it  is  true. 

In  an  entirely  different  way  the  chlorination  is  facilitated  by  the 
addition  of  red  phosphorus.  In  this  case,  phosphorus  pentachloride 
is  first  formed  from  the  phosphorus  and  chlorine  ;  this,  acting  on  the 
acetic  acid,  generates  acetyl  chloride,  and  this  latter,  with  an  excess 
of  the  acid,  forms  the  anhydride.  Direct  experiments  have  shown  that 
acid-chlorides,  as  well  as  anhydrides,  are  substituted  by  chlorine  with 
much  greater  ease  than  the  corresponding  acids  ;  in  this  fact  the  action 
of  red  phosphorus  finds  its  explanation.  Since  a  small  amount  of 
phosphorus  is  sufficient  for  the  chlorination  of  a  large  amount  of  acetic 
acid,  the  question  as  to  how  this  is  continuously  effected  remains  to  be 
answered.  In  accordance  with  the  above  statements,  the  following 
reactions  take  place  : 

(1)  P  +  C15  =  PC15 

(2)  CH3  .  CO  .  OH  +  PC15  =  CH3  .  CO  .  Cl  +  POC13  +  HC1 

CH3.CO\ 

CH 


(3)  CH..CO.C1  +  CH^.CO.OH=  >O  +  HC1 

,.CO/ 


1 66  SPECIAL  PART 

If  the  chlorine  now  acts  on  the  anhydride,  monochloracetic  anhydride 
is  formed : 

(4)  CH3.CO\  CH,C1.CO\ 

NV-V  ,  ri  -  \n  -i.  wn 

>U  +  L,12  =  /\J  T  rlLxl 

CH3.CO/  CH3.CO/ 

But  this  reacts  directly  with  the  hydrochloric  acid,  in  accordance  with 
this  equation : 

(5)  CH2C1.0X 

>0  +  HC1  =  CH9C1.CO.OH  +  CH,.CO.  Cl 

CHg.CO/ 

There  is  thus  obtained,  besides  the  molecule  of  chloracetic  acid,  the 
molecule  of  acetyl  chloride,  first  formed  in  reaction  2,  which  is  utilised 
repeatedly  by  its  regeneration  in  accordance  with  reactions  3,  4,  and  5. 

As  a  substitute  for  red  phosphorus,  sulphur  is  also  recommended 
for  the  chlorination  of  aliphatic  acids.  This  acts  in  a  wholly  similar 
manner,  since  it  first  forms  sulphur  chloride,  which,  reacting  on  the 
acid,  like  phosphorus  chloride,  converts  it  into  an  acid-chloride.  The 
other  phases  of  the  reaction  are  similar  to  those  given  above. 

The  bromination  of -aliphatic  carbonic  acids,  which  is  not  only 
of  great  importance  in  preparation  work,  but  also  as  a  means  for 
determining  constitution,  is  also  conducted  with  the  addition  of  red 
phosphorus  (Hell-Volhard-Zelinsky  Method).1 

The  halogen  atoms  always  enter  the  a-position  to  the  carboxyl 
group.  Thus,  e.g.,  when  proprionic  and  butyric  acids  are  brominated, 
they  yield : 

CH3.CHBr.CO.OH  CH3.CH2.CHBr.CO.OH 

a-Bromproprionic  a-Brombutyric  acid 

If  no  a-hydrogen  atom  is  present,  e.g.,  in  trimethyl-acetic  acid 
(CH3)3.C  .CO  .  OH,  bromination  will  not  take  place.  The  ability  of 

an  acid  to  form  a  bromine  substitution  product  can,  therefore,  be  used 
as  a  test  for  the  presence  of  an  a-hydrogen  atom.  Iodine  cannot  be 
introduced  directly  into  aliphatic  acids  like  chlorine  and  bromine.  To 
obtain  iodine  substitution  products,  it  is  necessary  to  treat  the  corre- 
sponding chlorine  or  bromine  compound  with  potassium  iodide  : 

CH2C1 .  CO .  OH  +  KI  =  CH2I .  CO  .  OH  +  KC1 

The  halogen  derivatives  of  the  fatty  acids  are  in  part  liquids,  in  part 
1  B.  14,  891 ;  21,  1726;  A.  242, 141 ;  B.  21.  1904;  B.  20,  2026;  B.  24,  2216. 


ALIPHATIC   SERIES  l6/ 

solids.  In  their  reactions  they  resemble  the  acids,  on  the  one  hand, 
since  they  form  salts,  chlorides,  anhydrides,  esters,  etc. ;  on  the  other 
hand,  the  halogen  alkyls.  They  are  of  great  value  in  the  preparation 
of  oxy-  and  amido-acids,  of  unsaturated  acids,  for  the  synthesis  of  poly- 
basic  acids,  etc.  Below  are  given  a  few  equations  capable  of  general 
application : 

CH2C1 .  CO  .  OH  +  H2O  =  CH2(OH).  CO .  OH  +  HC1 

Oxyacetic  acid  = 
Glycolic  acid 

CH2C1 .  CO .  OH  +  NH3  =  CH2 .  NH2 .  CO  .  OH  +  HC1 

Amidoacetic  acid  = 
Glycocoll 

CH2I  CH2 

CHo  +  KOH  =  CH  +KI  +  H9O 


COOH  CO.  OH 

(From  glyceric  acid  +  PI3)  Acrylic  acid 

CH2C1.CO.OH  +  KCN  =  CH2.CN.CO.OH  +  KC1 

Cyanacetic  acid 

CO.  OH 


CH, 


2CH2Br.CO.OH  +  Ag2=  |  +2AgBr 


.OH 

Succinic  Acid 


8.  REACTION:  OXIDATION  OP  A  PRIMARY  ALCOHOL  TO  AN 
ALDEHYDE 

EXAMPLE  :   Acetaldehyde  from  Ethyl  Alcohol * 

A  ij-litre  flask  containing  no  grammes  of  concentrated  sul- 
phuric acid  and  200  grammes  of  water  is  closed  by  a  two-hole 
cork ;  through  one  hole  passes  a  dropping  funnel,  through  the 
other  a  glass  delivery  tube  connected  with  a  long  condenser.  To 
the  lower  end  of  the  condenser  is  attached  an  adapter  bent  down- 
wards, the  narrower  portion  of  which  passes  through  a  cork  in 

IA.  14, 133;  j.  1853,329. 


1 68  SPECIAL  PART 

the  neck  of  a  thick-walled  suction  flask  of  about  ^-litre  capacity. 
(See  Fig.  65,  page  148.)  By  using  an  upright  coil  condenser  con- 
nected directly  with  the  suction  flask,  an  adapter  is  unnecessary. 
The  suction  flask  is  placed  in  a  water-bath  filled  with  a  freezing 
mixture  of  ice  and  salt.  The  larger  flask  is  heated  over  a  wire 
gauze  until  the  water  just  begins  to  boil ;  a  solution  of  200  grammes 
of  sodium  dichromate  in  200  grammes  of  water  which  has  been 
treated  with  100  grammes  of  alcohol  is  then  added  in  a  small 
stream  through  the  dropping  funnel,  the  lower  end  of  which  is 
about  3  cm.  above  the  surface  of  the  liquid  in  the  flask.  During 

the  addition  of  the  mixture,  it 
will  be  unnecessary  to  heat  the 
flask,  since  the  heat  produced 
by  the  reaction  is  sufficient 
to  cause  ebullition.  The  alde- 
hyde thus  formed  distils  into 
the  receiver,  besides  some  al- 
cohol, water,  and  acetal.  If 
uncondensed  vapours  of  the 
aldehyde  escape  from  the  re- 
ceiver, the  mixture  is  admitted 
to  the  flask  more  slowly.  On 

the  other  hand,  if  boiling  is  not  caused  by  the  flowing  in  of  the 
mixture,  the  reaction  is  assisted  by  heating  with  a  small  flame. 
After  all  of  the  mixture  has  been  added,  the  flask  is  heated  for  a 
short  time  by  a  flame,  until  boiling  begins. 

Since  the  aldehyde  cannot  be  obtained  easily  from  the  reaction- 
products  by  fractional  distillation,  it  is  first  converted  into  alde- 
hyde-ammonia, which,  on  proper  treatment,  readily  yields  the 
pure  aldehyde. 

The  apparatus  for  this  purpose  is  arranged  as  follows  :  A  small 
flask  to  contain  the  aldehyde,  placed  on  a  wire  gauze,  is  connected 
with  a  moderately  large  reflux  condenser.  Into  the  upper  end 
of  the  condenser  is  placed  a  cork  bearing  a  nL-shaped  glass  tube, 
which  is  connected  with  two  wash-bottles,  each  containing  50  c.c. 
of  dried  ether.  After  the  condenser  has  been  filled  with  water  at 


ALIPHATIC  SERIES  169 

30°  (the  lower  side-tube  of  the  condenser  is  closed  with  rubber 
tubing  and  a  pinch-cock),  the  crude  aldehyde  is  heated  for  5-10 
minutes  to  gentle  boiling,  and  the  aldehyde  that  is  not  condensed 
passes  over,  and  is  absorbed  by  the  ether.  Should  the  ether  begin 
to  ascend  in  the  connecting  tube,  the  flame  must  be  somewhat 
increased  immediately.  To  obtain  aldehyde-ammonia,  a  current 
of  dry  ammonia  (see  page  382)  is  conducted,  with  the  aid  of  a 
wide  adapter  or  funnel  (Fig.  66),  into  the  ethereal  solution  con- 
tained in  a  beaker  surrounded  by  a  freezing  mixture  of  ice  and  salt, 
until  the  liquid  smells  strongly  of  it.  After  an  hour,  the  aldehyde- 
ammonia  which  has  separated  out  is  scraped  from  the  sides  of  the 
vessel  and  adapter  with  a  spatula  or  knife,  filtered  with  suction, 
washed  with  a  little  ether,  and  then  allowed  to  dry  on  filter-paper 
in  a  desiccator.  Yield,  about  30  grammes. 

In  order  to  obtain  pure  aldehyde,  10  grammes  of  aldehyde- 
ammonia  are  dissolved  in  10  grammes  of  water,  treated  with  a 
cooled  mixture  of  15  grammes  of  concentrated  sulphuric  acid 
and  20  grammes  of  water,  and  heated  on  the  water-bath.  Since 
aldehyde  has  a  low  boiling-point  (21°),  the  receiver  is  connected 
with  the  condenser  by  a  cork,  and  well  cooled  with  ice  and  salt. 

Aldehydes  can  be  obtained  by  the  use  of  the  general  reaction,  which 
in  many  cases  serves  as  a  method  of  preparation,  of  extracting  two 
hydrogen  atoms  from  a  primary  alcohol  by  oxidation. 

/H 

CH3.CH2.OH  +  O  =  CH3.C^      +  H0O 

^O 

The  name  of  th.e  class  of  compounds  is  derived  from  this  action  :  Alde- 
hyde =  Al(cohol)dehyd  (rogenatus).  As  an  oxidising  agent  in  the 
above  case,  chromic  acid  is  the  most  suitable  in  the  form  of  potassium, 
or  sodium  dichromate  in  the  presence  of  sulphuric  acid  : 

Na2Cr2O7  +  4  H2SO4  =  O3  +  (SO4)3Cr2  +  Na2SO4  +  4  H2O 

The  rather  difficultly  soluble  potassium  dichromate  (i  part  dissolves  in 
10  parts  water)  was  formerly  generally  used,  but  at  present  the  more  sol- 
uble and  cheaper  sodium  salt  (i  part  dissolves  in  3  parts  of  water)  is  em- 
ployed wherever  it  is  possible.  But  in  the  preparation  of  the  simplest 
aldehyde  (formaldehyde)  from  an  alcohol  a  different  oxidising  agent  is 


SPECIAL  PART 

used,  viz.  the  oxygen  of  the  air.  On  passing  a  mixture  of  the  vapour 
of  methyl  alcohol  and  air  over  a  heated  copper  spiral,  formaldehyde  is 
produced. 

While  by  the  first  reaction  one  proceeds  from  substances  which  in 
comparison  with  the  aldehydes  are  oxidation  products  of  a  lower  order, 
the  aldehydes  may  also  be  obtained  by  a  second  method  involving  the 
use  of  compounds  of  the  same  substitution  series,  viz.  the  dihalogen 
derivatives  of  the  hydrocarbons  containing  the  group  CHC12  or  CHBr2. 
If  these  are  boiled  with  water,  or,  better,  water  containing  sodium  car- 
bonate, potash,  lead  oxide,  or  calcium  carbonate,  etc.,  the  two  halogen 
atoms  are  replaced  by  one  oxygen  atom  : 

CH8.CHC12  +  H2O  =  CH3.CHO  +  2.  HC1 

Ethylidene  chloride 

C6H5.CHC12  +  H20  =  C6H5.CHO  +  2  HC1 

Ben/ylidene  chloride  =  Benzaldehyde 

Benzalchloride 

This  method  is  used  on  the  large  scale  for  the  manufacture  of  the  com- 
mercially important  benzaldehyde.  It  will  be  referred  to  under  benzal- 
dehyde. 

Finally,  aldehydes  can  be  prepared  from  their  oxidation  products, 
the  carbonic  acids,  by  two  methods,  one  of  which  has  been  already 
mentioned  under  acetic  anhydride.  If  sodium  amalgam  is  allowed  to 
act  on  acid-anhydrides,  an  aldehyde  is  first  formed  : 


CH3.CO 
CH 


3. 

>0  +  H2  =  CH3.CHO  +  CHg.CO.OH 
3.CO/ 


But  this  reaction  is  of  little  practical  value  for  the  preparation  of  alde- 
hydes. The  second  method,  which  is  the  real  preparation  method, 
consists  in  the  dry  distillation  of  a  mixture  of  the  calcium  or  barium 
salt  of  the  acid  with  calcium  or  barium  formate  : 

CH3.CO.Oca  +  H.  CO.  Oca  =  CH3.CHO  +  CaCO 

(ca  = 


The  lower  members  of  the  aldehyde  series  are  colourless  liquids,  soluble 
in  water,  possessing  pungent  odours.  The  intermediate  members  are 
also  liquids,  but  insoluble  in  water  ;  the  higher  members  are  solid,  crys- 
tallisable  substances.  The  boiling-points  of  the  aldehydes  are  lower 
than  those  of  the  corresponding  alcohols. 


ALIPHATIC  SERIES  I /I 

jCHg.CHO Boiling-point,  21° 

<CH3.CH2.OH «           "78° 

fCH3.CH2.CHO "           "50° 

lCH3.CH2.CH2.OH    ....  «           "     97° 

Aldehydes  are  oxidised  to  acids  by  free  as  well  as  combined  oxygen 
(compare  benzaldehyde)  : 

CH3.CHO  +  O  =  CH3.CO.OH 

Upon  this  action  depends  the  fact  that  aldehydes  cause  metals  to  sepa- 
rate from  certain  salts,  e.g.  silver  nitrate : 

CH, .  CHO  +  Ag20  =  CH3 .  CO .  OH  +  Ag,,1 

EXPERIMENT  :  Treat  a  few  cubic  centimetres  of  a  diluted  silver 
nitrate  solution  with  a  few  drops  of  ammonium  hydroxide  and  5 
drops  of  aldehyde.  Silver  will  be  deposited  in  the  form  of  a  brill- 
iant mirror  on  the  walls  of  the  vessel ;  the  deposition  is  especially 
beautiful  if  the  vessel  has  previously  been  treated  with  a  solution 
of  caustic  soda  to  remove  any  fatty  matter.  The  reaction  fre- 
quently takes  place  at  the  ordinary  temperature,  but  in  many 
cases  only  on  gentle  warming.  The  reaction  is  used  for  the 
detection  of  aldehydes. 

Another  reaction  which  can  also  be  employed  for  the  recognition  of 
aldehydes,  depends  upon  the  fact  that  they  give  a  red  colour  to  fuchsine- 
sulphurous  acid.  (Caro's  reaction.) 

EXPERIMENT  :  Fuchsine-sulphurous  acid  is  prepared  by  dissolv- 
ing fuchsine  in  water ;  a  sufficient  quantity  of  the  latter  is  taken 
to  prevent  the  solution  from  being  too  intense  in  colour.  Sulphur 
dioxide  is  conducted  into  this  until  a  complete  decolouration  takes 
place.  To  a  few  cubic  centimetres  of  this  solution  add  several  drops 
of  aldehyde.  On  shaking,  a  violet-red  colour  will  be  produced. 

Finally  aldehydes  may  also  be  detected  by  a  method  depending  upon 
the  fact  that  when  treated  with  diazobenzene  sulphonic  acid  and  sodium 
amalgam,  they  give  a  violet  colour. 

EXPERIMENT  :  To  as  much  diazobenzene  sulphonic  acid  as  can 
be  held  on  the  point  of  a  knife,  add  5  c.c.  of  water,  a  few  drops 

1  B.  15,  1635  and  1828. 


\J2  SPECIAL  PART 

of  caustic  soda,  and  then  a  few  drops  of  aldehyde,  and  finally  a 
piece  of  solid  sodium  amalgam  as  large  as  a  pea.  After  some 
time  the  red-violet  colour  appears. 

That  aldehydes  upon  reduction  pass  over  to  primary  alcohols  has 
been  mentioned  under  acetic  anhydride : 

CH3 .  CHO  +  H2  =  CH3 .  CH2 .  OH 

It  is  wholly  characteristic  of  the  aldehydes  that  they  unite  directly 
(i)  with  ammonia,  (2)  sodium  hydrogen  sulphite,  and  (3)  hydrocyanic 
acid.  The  union  with  ammonia  takes  place  in  accordance  with  the 
following  equation : 

CHo.CHO  +  NH3  =  CH3.CH<^ 

\NH2 

Aldehyde-ammonia= 
a-amidoethyl  alcohol 

This  reaction  is  not  so  common  as  the  second  and  third.  Thus, 
e.g.,  formic  aldehyde  and  most  of  the  aromatic  aldehydes  behave 
differently  toward  ammonia.  Whenever  this  reaction  does  take  place 
it  can  also  be  used  with  advantage  for  the  purification  of  the  aldehyde, 
as  in  case  of  acetaldehyde ;  by  allowing  the  well -crystallised  double 
compound  to  separate  out,  on  treating  it  with  dilute  sulphuric  acid,  the 
free  aldehyde  is  obtained. 

The  union  with  sodium  hydrogen  sulphite  takes  place  in  accordance 
with  the  following  equation : 

/OH 
CH3.CHO  +  SO3NaH  =  CH3.CH< 

\S03Na 

Sodium-a-oxyethyl  sulphonate 

This  reaction  may  also  be  used  for  the  purification  of  aldehydes, 
since  when  a  concentrated  solution  of  the  sulphite  is  employed,  the 
double  compound  generally  separates  out  in  a  crystallised  condition. 
The  free  aldehydes  can  be  obtained  from  the  sulphite  compounds  by 
heating  with  dilute  acids  or  alkali  carbonates.  (Compare  benzalde- 
hyde.) 

EXPERIMENT  :  Treat  5  c.c.  of  a  cooled  concentrated  solution  of 
sodium  hydrogen  sulphite  with  i  c.c.  of  aldehyde  and  shake  the 
mixture.  The  double  compound  separates  out  in  a  crystallised 
condition. 


ALIPHATIC  SERIES  1/3 

As  distinguished  from  the  union  of  aldehyde  with  ammonia,  this  re- 
action is  wholly  general,  and  is  frequently  of  great  value  in  dealing  with 
the  aldehydes  of  the  aromatic  series.  It  should  be  noticed  in  this  con- 
nection, that  the  ketones,  which  are  closely  related  to  the  aldehydes, 
show  similar  reactions : 

CH3 

I  /OH      . 
CH3.CO.CH3  +  SO3NaH  =  C< 

Acetone  I     \SOoNa 


The  addition  of  hydrocyanic  acid  to  ketones  as  well  as  to  aldehyde? 
is  also  general : 

/OH 
CHo.CHO  +  HCN  =  CH3.CH< 

\CN 

a-oxyproprionitrile 

This  reaction  is  of  especial  interest,  since  the  addition  of  a  new 
carbon  atom  is  brought  about.  Concerning  the  value  of  this  reaction 
for  the  synthesis  of  a-oxyacids,  see  Mandelic  Nitrile,  page  307. 

Aldehydes  possess  further  a  marked  tendency  to  combine  with  them- 
selves (polymerise). 

EXPERIMENT  :  Treat  i  c.c.  of  aldehyde  with  one  drop  of  con- 
centrated sulphuric  acid.  The  aldehyde  boils,  and  polymerisation 
(condensation)  takes  place. 

The  compound  thus  obtained  is  called  paraldehyde ;  it  boils  much 
higher  (124°)  than  ordinary  aldehyde;  the  determination  of  its  vapour 
density  shows  that  one  molecule  is  composed  of  three  molecules  of 
ordinary  aldehyde.  Paraldehyde  does  not  show  the  characteristic  alde- 
hyde reactions  ;  on  distillation  with  dilute  sulphuric  acid  it  is  converted 
back  into  the  ordinary  variety.  For  this  reason  it  is  believed  that  no 
new  union  of  carbon  atoms  takes  place  in  the  molecule,  but  that  three 
molecules  are  united  by  means  of  the  oxygen  atoms : 

O  -  CH— CH3 


CH3.CH<^  No 


O  -  CH— CH3 

If  aldehyde  is  cooled  and  treated  with  sulphuric  acid,  or  if  at  the 
ordinary  temperature  gaseous  hydrochloric  acid,  sulphur  dioxide,  or 
other  compounds  are  passed  into  it,  a  solid  polymerisation  product, 


1/4  SPECIAL   PART 

metaldehyde,  is  formed;  this  can  also  be  converted  back  into  the  ordi- 
nary variety. 

The  aldehydes  undergo  a  wholly  different  kind  of  polymerisation 
under  certain  conditions,  concerning  which  reference  must  be  made  to 
the  chemical  literature  and  treatises.  For  example,  two  molecules  ot 
acetaldehyde  can  unite  with  the  formation  of  a  compound  in.  which  a 
new  carbon  union  is  present. 

CH3.CHO  +  CH3.CHO  -  CH3.CH(OH)  .CH2.CHO 

Aldol 

This  compound,  as  distinguished  from  paraldehyde  and  metaldehyde, 
is  a  true  aldehyde,  in  that  it  cannot  be  converted  back  to  acetalde- 
hyde. Aldol  loses  water  easily,  and  is  converted  into  an  unsaturated 
aldehyde  : 

CH3  .  CH(OH)  .  CH2.  CHO  =  CH3  .  CH=CH  .  CHO  -f-  H2O 

Crotonaldehyde 

In  connection  with  these  condensations,  it  may  be  pointed  out  that 
many  aldehydes,  when  heated  with  alkalies,  polymerise  to  resinous 
products  of  high  molecular  weight  (aldehyde  resins). 

EXPERIMENT  :  Treat  a  few  cubic  centimetres  of  caustic  potash 
solution  with  several  drops  of  aldehyde,  and  warm.  A  yellow 
colouration  takes  place  with  the  separation  of  a  resinous  mass. 

In  order,  finally,  to  represent  the  great  activity  of  the  aldehydes,  the 
following  equations  are  given  : 

CH3  .  CHO  +  PC15  =  CH3  .  CHC12  +  POC13 

Ethyhdene  chloride 

CH3.CHO  +  NH2.OH  =CH3.CH=NOH  +  H2O 

Aldoxime 

CH3.CHO  +  NH2.NH.C6H5  =  CH3.CH—  N.NH.C6H5  -f-  H2O 

Phenylhydrazine  Hydrazone  of  aldehyde 

OC2H5 

CH3  .  CHO  +  2  C2H5  .  OH         =  CH3  .  CH<(  -f  H2O 

XOC2H5 

f        Acetal,  the  ether  of  aldehyde-        "I 

hydrate  CH3  .  CH  <  §g  which  does 

[        not  exist  in  the  free  condition        J 

/C6H5 

CH3  .  CHO  +  2  C6H6  =  CH3  .  CH/          +  H2O 


Diphenyl  ethane 


ALIPHATIC  SERIES  175 


9.  REACTION :  PREPARATION  OP  A  PRIMARY  AMINE  FROM  AN 
ACID-AMIDE  OF  THE  NEXT  HIGHER  SERIES 

EXAMPLE  :   Methyl  Amine  from  Acetamide 1 

To  a  mixture  of  25  grammes  of  acetamide,  which  has  been 
previously  well  pressed  out  on  a  porous  plate,  and  70  grammes 
(23  c.c.)  of  bromine  contained  in  a  J-litre  flask,  add  a  solution  of 
40  grammes  of  caustic  potash  in  350  c.c.  of  water  (the  flask  is  well 
cooled  with  water),  until  the  brownish  red  colour  formed  at  first  is 
changed  to  a  bright  yellow,  for  which  the  greater  portion  of  the 
potash  solution  will  be  required.  This  reaction:mixture  is  then, 
in  the  course  of  a  few  minutes,  allowed  to  flow  from  a  dropping 
funnel  in  a  continuous  stream  into  a  litre  flask  containing  a  solution 
of  80  grammes  of  caustic  potash  in  150  c.c.  of  water  heated  to 
70-75°.  In  case  the  temperature  rises  higher  than  75°,  the  flask 
must  be  cooled  by  immersion  for  a  short  time  in  cold  water.  The 
liquid  is  maintained  at  this  temperature  until  it  becomes  colourless, 
which  usually  requires  a  quarter  to  half  hour.  The  methyl  amine 
is  then  distilled  off  with  steam,  and  collected  in  a  receiver  contain- 
ing a  mixture  of  60  grammes  of  concentrated  hydrochloric  acid 
and  40  grammes  of  water.  In  order  that  the  methyl  amine  may 
be  completely  absorbed  by  the  acid,  the  end  of  the  condenser  is 
connected  with  an  adapter  which  dips  i  cm.  below  the  surface  of 
the  liquid  in  the  receiver.  If  a  coil  condenser  is  employed,  the 
end  of  it  dips  directly  into  the  acid.  As  soon  as  the  liquid  in  the 
condenser  no  longer  shows  an  alkaline  reaction,  the  distillation  is 
discontinued.  The  methyl  amine  hydrochloride  is  partially  evapo- 
rated in  a  porcelain  dish  over  a  free  flame,  then  to  dryness  on  the 
water-bath,  and  is  finally  heated  for  a  short  time  in  an  air-bath  at 
1 00°  to  dusty  dryness.  In  order  to  separate  the  methyl  amine 
salt  from  the  ammonium  chloride  mixed  with  it,  the  finely  pul- 
verised substance  is  crystallised  from  absolute  alcohol,  and  the 
crystals  separating  out  dried  in  a  desiccator.  Yield,  varying. 

1  B.  15,  762 ;  B.  17,  1406  and  1920. 


176  SPECIAL  PART 

Under  the  discussion  of  acid-amides,  it  has  already  been  mentioned 
that  the  hydrogen  of  the  amido  group  (NH2)  can  be  substituted  by 
bromine.  If  a  10  %  solution  of  caustic  potash  is  added  to  a  mixture 
of  one  molecule  of  the  amide  and  one  molecule  of  bromine,  until  the 
brownish  red  colour  of  the  latter  has  vanished,  a  monobromamide  is 
formed,  e.g.,  in  the  above  case,  acetmonobromamide  in  accordance 
with  this  equation : 

CH, .  CO  .  NH2  +  Br2  +  KOH  =  CH3  .  CO  .  NHBr  +  KBr  +  H2O 
The  monobromamide  may  be  isolated  in  pure  condition  in  the  form 
of  colourless,  hydrous  crystals.     If  hydrobromic  acid   is  abstracted, 
no  water  being  present,  the  position  of  the  carbonyl  group   (CO)  is 
changed,  and  an  ester  of  isocyanic  acid  is  formed : 

CH, .  CONHBr  =  CH3  .  N=CO  +  HBr 

Methyl  isocyanate 

If  the  attempt  is  made  to  eliminate  hydrobromic  acid  in  the  presence 
of  water  by  the  use  of  caustic  potash  solution,  the  above  reaction  takes 
place,  but  the  isocyanate  is  unstable  in  the  presence  of  alkalies,  and 
decomposes  immediately  by  taking  up  the  water  forming  carbon  dioxide 
and  a  primary  amine  : 

CH3  .  NCO  +  H2O  =  C02  +  CH, .  NH2 

Methyl  amine 

The  two  reactions  may  also  be  simply  expressed  as  follows : 
CH3  .  CO  .  NH2  +  O  =  CH3  .  NH2  +  CO2 

Bromine  + 
alkali 

This  reaction,  discovered  by  A.  W.  Hofmann,  is,  therefore,  in  its  last 
phase,  identical  with  the  historical  reaction  of  Wurtz,  which  led  him, 
in  1848,  to  the  discovery  of  the  primary  amines. 

The  Hofmann  reaction  is  capable  of  general  application.  By  use  of 
it,  the  primary  amine  of  the  next  lower  series  may  be  obtained  from 
any  acid-amide,  since  the  elimination  of  carbon  dioxide  takes  place. 
With  the  higher  members  of  the  series,  the  reaction  in  part  proceeds  still 
further,  since  the  bromine  acts  upon  the  primary  amine  to  form  a  nitrile  : 
C7H15.CH2.  NH2  +  Br4+  4NaOH  =  C7H15.  C=N  +  4NaBr  +  4H2O 

Octyl  amine  Octonitrile 

There  is  thus  obtained  from  the  higher  members  (compounds  having 
five  or  more  carbon  atoms)  of  the  amides,  first  the  primary  amine,  and 
secondly,  the  nitrile  of  the  next  lower  acid.  In  the  aromatic  series,  the 
reaction  for  the  preparation  of  primary  amines,  which  contain  the  amido 
group  in  the  benzene  ring,  is  not  of  general  importance,  since  these 


ALIPHATIC  SERIES  177 

may  be  obtained  from  the  easily  accessible  nitro-compounds  ;  and 
since,  on  the  other  hand,  if  the  above  reaction  is  employed,  bromine 
substitution  products  are  easily  formed.  But  in  those  cases  in  which 
the  nitro-compound  corresponding  to  the  amine  is  not  known,  or  can 
be  prepared  only  with  difficulty,  the  reaction  is  also  of  importance  in 
the  aromatic  series.  Two  cases  of  this  kind  may  be  mentioned  in  this 
place.  If  phenyl  acetamide  is  treated  in  accordance  with  Hofmann's 
reaction,  there  is  formed  in  the  usual  way  benzyl  amine  : 

C6H,  .  CH2  .  CO  .  NH2  +  O  =  C6H5  .  CH2  .  NH2  +  CO2 

Phenyl  acetamide  Benzyl  amine 

Further,  the  reaction  is  of  practical  value  in  the  preparation  of  o-amido- 
benzoic  acid,  used  in  the  manufacture  of  artificial  indigo.  If,  as  above, 
bromine  and  caustic  potash  are  allowed  to  act  on  phthalimide  (techni- 
cally bleaching  powder  is  used),  there  is  first  formed,  by  the  addition 
of  water,  an  acid-amide  : 

OK  CO  .  NH9 


/OK  / 

o-C6H4<          >NH  +  H20  =  C6H4< 
\CO/  \ 


CO  .  OH 

which  in  accordance  with  the  following  reactions  gives  the  amido-acid. 

/CO  .  NH2  /CO  .  NHBr 

HBr 


C6H  +  Br2    =  C6H4< 

\CO  .  OH  \CO  .  OH 

/CO  .NHBr  /N=C=z  O 

C6H4<  =  C6H4< 

\ 

/NH 
/ 


64  +  HBr 

\CO  .  OH  \CO  .  OH 


+  H20  =  C6H  /  +  C02 

D  .  OH  \CO  .  OH 

Since  the  nitro-acid  corresponding  to  the  o-amido  benzoic  acid  is  dif- 
ficult to  obtain,  and  phthalimide  is  easily  prepared  (naphthalene  is 
changed  to  phthalic  anhydride  by  oxidation,  and  when  this  is  treated 
with  ammonia,  phthalimide  is  formed  with  the  separation  of  water),  the 
Hofmann  reaction  in  this  case  gives  a  very  convenient  method  of  prep- 
aration fcr  the  amido-acid. 

Primary  aliphatic  amines  can  also  be  prepared  according  to  the  fol- 
lowing equations  : 

(i)  By  the  action  of  alcoholic  ammonia  on  halogen  alkyls  : 

CH8I  +  NHS  =  CH3 .  NH2  4-  HI 

In  this  case,  secondary  and  tertiary  bases,  or  the  corresponding  ammo 
nium  compounds,  are  also  formed. 

N 


178  SPECIAL  PART 

(2)  From  alcohols  and  zinc  chloride-ammonia : 

C2H5.OH  +  NH3  =  C2H5.NH2  +  H2O 

(3)  By  the  reduction  of  nitriles  (Mendius1  reaction)  : 

CHg.CN  +  2H2  =  CH3.CH2.NH2 

(4)  By  the  reduction  of  nitro-compounds : 

CH3.NO2  +  3H2  =  CH3.NH2  +  2H2O 

(5)  By  the  reduction  of  oximes  and  hydrazones : 

CH3.CH=N.OH  +  2  H2  =  CH3.CH2.NH2  +  H2O 

Acetaldoxime 

CH3 .  CH=N  -  NH .  C6H5  +  2  H2  =  CH3 .  CH2 .  NH2  +  C6H5 .  NH2 

Ethylidene  phenyl  hydrazone  Aniline 

The  lowest  members  of  the  amines  in  the  free  condition  are  gaseous 
compounds  soluble  in  water,  possessing  odours  suggestive  of  ammonia : 
they  differ  from  ammonia  in  being  inflammable. 

EXPERIMENT  :  Treat  some  solid  methyl  amine  hydrochloride  in 
a  small  test-tube  with  a  concentrated  solution  of  caustic  potash,  or 
caustic  soda,  and  warm  gently.  A  gas,  smelling  like  ammonia,  is 
evolved,  which  burns  with  a  pale  flame. 

The  higher  members  are  liquids  or  insoluble  solids.  Since  they  are 
derivatives  of  ammonia,  they  possess  basic  properties,  and,  like  ammo- 
nia, unite  with  acids  to  form  salts,  the  composition  of  which  is  analo- 
gous to  that  of  the  ammonium  compounds  : 

NH3 .  HC1 >-  CH3 .  NH2 .  HC1 

(NH4Cl)2PtCl4 ^(CH3.NH2.HCl)2PtCl4 

NH4C1,  AuCl3 ^CH8.NH2.HC1,  AuCl3 

The  hydrochlorides  of  organic  bases  are  distinguished  from  ammonium 
chloride  by  their  solubility  in  absolute  alcohol.  Use  was  made  of  this 
property  above. 

The  numerous  reactions  of  the  primary  amines*  need  not  be  men- 
tioned here,  since,  under  the  aromatic  amines,  frequent  reference  will 
be  made  to  them.  At  this  place,  one  difference  between  the  aromatic 
and  aliphatic  amines  will  be  pointed  out.  If  nitrous  acid  is  allowed  to 


ALIPHATIC  SERIES  179 

act  on  an  aliphatic  primary  amine,  an  alcohol  is  formed  with  evolution  of 
nitrogen  :       CRg  ^  +  NQOH  =  ^ .  OH  +  N2  +  H2O 

while,  under  these  conditions,  an  aromatic  amine  is  converted  into  a 
diazo-compound  (see  Diazo-compounds). 

10.   REACTION:  SYNTHESES  OF  KETONE  ACID-ESTERS  OR 
POLYKETONES  WITH  SODIUM  OR  SODIUM  ALCOHOLATE 

EXAMPLE  :   Acetacetic  Ester  from  Acetic  Ester  and  Sodium 1 

For  .the  successful  preparation  of  acetacetic  ester,  the  character 
of  the  acetic  ester  used  is  of  great  importance,  since,  if  it  is  com- 
pletely free  from  alcohol,  it  will  be  attacked  very  slowly  by  sodium, 
even  on  heating ;  if,  on  the  other  hand,  it  contains  too  much  alco- 
hol, the  sodium  acts  easily,  but  the  yield  of  the  product  is  varying 
and  usually  small.  According  to  the  experiments  of  the  author, 
the  following  method  of  procedure  gives  a  good  yield  and  is  one 
that  does  not  fail. 

Purification  of  Acetic  Ester :  The  acetic  ester  prepared  accord- 
ing to  Reaction  6,  even  after  it  has  been  freed  from  acetic  acid 
and  alcohol  by  shaking  with  sodium  carbonate  and  calcium  chloride 
respectively,  dried  over  calcium  chloride,  and  finally  rectified,  is 
not  suitable  for  this  preparation,  since  it  reacts  too  violently  with 
sodium.  But  if  it  is  allowed  to  stand,  after  distilling,  for  some 
hours,  over  night  at  least,  in  a  well-closed  flask,  over  about  \  its 
volume  of  granulated  calcium  chloride,  and  is  then  filtered,  it  may 
be  used  for  the  successful  preparation  of  acetacetic  ester. 

If  commercial  acetic  ester  is  to  be  used,  it  must  be  shaken  with 
a  sodium  carbonate  solution,  as  described  on  page  157,  treated 
with  calcium  chloride  solution,  etc. ;  in  short,  it  is  treated  as  the 
crude  product  obtained  in  the  preparation  of  acetic  ester.  Ob- 
viously, it  is  also  necessary  to  allow  it  to  stand  over  night  in 
contact  with  calcium  chloride,  after  the  distillation. 

The  yield  of  acetacetic  ester  may  be  further  increased  if  the 
acetic  ester,  after  being  filtered  from  the  calcium  chloride,  is  again 
distilled,  care  being  taken  to  prevent  the  absorption  of  moisture. 
All  parts  of  the  apparatus  must  be  perfectly  dried,  and  the  end  of 

1  A.  186,  214. 


l8o  SPECIAL  PART 

the  condenser  tube  must  be  connected  to  the  receiver  (suction* 
flask)  by  a  good  cork. 

Preparation  of  Acetacetic  Ester:  25  grammes  of  sodium  from 
which  the  outside  layers  have  been  removed  are  cut  with  the  aid 
of  a  sodium  knife  (Fig.  89)  into  pieces  as  thin  as  possible,  and 
placed  in  a  dry  litre-flask.  After  this  is  connected  with  a  long 
reflux  condenser,  inclined  at  an  oblique  angle,  250  grammes  of 
dried  acetic  ester  is  poured  into  the  top  of  the  condenser,  by  a 
funnel  which  must  not  be  attached  to  the  condenser,  but  is 
held  in  the  hand,  so  that  the  air  may  escape.  If  the  acetic  ester 
is  added  properly,  no  violent  ebullition  will  occur,  but  at  first  a 
gradual,  gentle  boiling.  After  10  minutes,  the  flask  is  placed  on 
a  previously  heated  water-bath,  the  temperature  of  which  is  so 
regulated  that  the  acetic  ester  boils  but  gently;  the  reaction- 
mixture  is  heated  until  all  the  sodium  is  dissolved,  which  will 
require  from  3-4  hours.  To  the  warm  liquid  is  added  a  mixture 
of  80  grammes  of  glacial  acetic  acid  and  80  grammes  of  water, 
until  it  just  shows  an  acid  reaction.  If  a  thick,  porridge-like 
mass  should  separate  out,  this  is  again  dissolved  by  vigorous 
shaking,  or  carefully  breaking  up  the  small  lumps  with  a  glass 
rod.  To  the  liquid  is  then  added  an  equal  volume  of  a  cold 
saturated  solution  of  sodium  chloride,  and  the  lower  aqueous  layer 
is  separated  from  the  upper  one,  consisting  of  acetic  ester  and 
acetacetic  ester,  by  allowing  it  to  run  off  from  a  dropping  funnel. 
Should  a  precipitate  settle  out  on  the  addition  of  the  salt  solution, 
it  is  dissolved  by  adding  some  water.  To  separate  the  acetacetic 
ester  from  the  main  portion  of  the  excess  of  the  acetic  ester  used, 
the  mixture  is  distilled  from  a  flask,  heated  by  a  free  flame  over 
a  wire  gauze,  or,  more  conveniently,  without  the  wire  gauze,  with  a 
luminous  flame.  As  soon  as  the  thermometer  indicates  95°,  the 
heating  is  discontinued,  and  the  residue  is  subjected  to  vacuum- 
distillation,  as  described  on  page  25 .  In  place  of  the  usual  con- 
denser, the  outside  jacket  of  a  Liebig  condenser  is  pushed  over 
the  long  side-tube  of  the  distillation  flask,  and  water  is  allowed 
to  circulate  through  it.  The  heating  is  done  in  an  air-bath. 
After  small  quantities  of  acetic  ester,  water,  and  acetic  acid  have 


ALIPHATIC   SERIES  l8l 

passed  over,  the  temperature  becomes  constant,  and  the  main 
portion  of  the  acetacetic  ester  distils  over  within  one  degree. 
The  following  table  gives  the  boiling-points  at  various  pressures, 
A  reference  to  this  will  show  at  what  approximate  points  the  col- 
lection of  the  preparation  should  begin  : 

Boiling-point    71°  at  12.5  mm.  pressure. 

"  74°  "  14  "  " 

"  79°  "  1 8  "  " 

"  88°  "  29  "  " 

94°  "  45  " 

97°  "  59  " 

"  100°  "  80  "  " 

The  yield  of  acetacetic  ester  amounts  to  55-60  grammes. 

In  the  preparation  of  this  substance,  it  must  be  borne  in  mind 
that  the  experiment  must  be  completed  in  one  day.  The  opera- 
tion should  be  begun  in  the  morning,  the  acetic  ester  heated  with 
sodium  at  midday,  and  the  experiment  completed  in  the  afternoon. 
If  the  reaction  is  discontinued  at  any  point,  and  the  unfinished 
preparation  allowed  to  stand  over  night,  the  yield  is  materially 
diminished. 

The  formation  of  acetacetic  ester  from  acetic  ester,  discovered  by 
Geuther  in  1863,  takes  place  in  accordance  with  the  following  equation : 


CH3 .  CO  |OC2H5  +  H.I  CH2 .  CO .  OC2H5 

=  CH3.CO.CH2.COOC2H5  +  C2H5.OH 

Acetacetic  ester 

But  the  mechanism  of  the  reaction  is  much  more  complicated  than 
here  indicated.  .  According  to  the  views  of  Claisen,  the  sodium  first 
acts  on  the  alcohol,  which,  as  above  mentioned,  must  be  present  in 
small  quantities,  forming  sodium  alcoholate,  and  this  unites  with  the 

acetic  ester  as  follows  : 

X)C2H5 

CH3.CO.OC2H3  +  C,H..ONa  =  CHo.C^-OC2H5 

\ONa 

Reaction  then  takes  place  between  this  addition  product  and  a  second 
molecule  of  acetic  ester,  with  the  elimination  of  two  molecules  of  alcohol, 
and  the  formation  of  the  sodium  salt  of  the  acetacetic  ester : 


1 82  SPECIAL  PART 


ONa  =  CH3.C=CH.CO.OC2H5  +  2C2H5.OH 


ONa 

On  acidifying  with  acetic  acid,  the  sodium  salt  is  decomposed  with 
the  formation  of  the  free  ester,  CH3.CzzCH  .CO.OC2H5  (enolform), 

OH 

which  spontaneously  changes  into  the  desmotropic  form  (ketoform).1 

CH3.CO.CH2.CO.OC2H5. 

In  the  form  indicated  above,  the  reaction  is  not  capable  of  general 
application ;  but  a  reaction  closely  related  to  it,  discovered  by  Claisen 
and  W.  Wislicenus,  is  of  general  applicability,  and  is  of  great  value  in 
synthetical  operations;  for  this  reason  it  will  be  briefly  mentioned 
here.  If  sodium  alcoholate  is  allowed  to  act  on  a  mixture  of  the  esters 
of  two  monobasic  acids,  a  ketone  acid-ester,  having  a  constitution  anal- 
ogous to  that  of  acetacetic  ester,  is  formed  by  the  action  of  the  sodium 
alcoholate  on  one  of  the  esters  with  the  elimination  of  alcohol,  e.g. : 
C6H5 .  CO  |OC2H5  +  H|  CH2 .  COOC2H5 

Benzoic  ester  Acetic  ester 

=  C6H5 .  CO .  CH2 .  CO .  OC2H5  +  C2H5 .  OH 

Benzoyl  acetic  ester 

If  one  of  the  compounds  is  formic  ester,  esters  of  aldehyde-acids  will 
be  obtained,  e.g. : 


H.CO.  |OC2H5  +  H|CH2.CO.OC2H5  =  H.CO.CH2.CO.OC2H5 

Formic  ester  Acetic  ester  Formyl  acetic  ester 

If  one  molecule  of  a  dibasic  ester  is  used,  a  ketone  dicarbonic  acid 
ester  will  be  formed,  e.g. : 


CO .  |OC2H5      H| .  CH2 .  CO .  OC2H5    CO .  CH2 .  CO .  OC2H5 

+  =  I  -f  C2H5.OH 

CO.OC2H3  CO.OC2H5 

Oxalic  ester  Acetic  ester  Oxalacetic  ester 

In  place  of  the  acid-ester  in  the  above  reaction,  which  is  susceptible 
of  many  combinations,  a  ketone  may  be  used ;  a  ketone  acid-ester  is 
not  formed,  it  is  true,  but  polyketones,  or  ketone-aldehydes : 


CH3 .  CO  |OC2H5  +  H|  CH2 .  CO .  CH8 

Acetic  ester  Acetone 

=  CH3.CO.CH2.CO.CH3  +C2H5.OH 

_    Acetylacetone 

1  B.  31,  205,  and  601. 


ALIPHATIC   SERIES  183 


C6H5.CO  OC2H5  +  H.  CH2.CO.CH 


Benzole  ester  -  CgH5 .  CO  .  CH2 .  CO  .  CH3  +  C2H5 .  OH 

Benzoylacetone 

H.CO.  JOC2H5  +  H.|CH2.CO.C6H5 

Formic  ester  Acetophenone 

=  O=CH .  CH2 .  CO .  C6H5  +  C2H5 .  OH 

Benzoylaldehyde 

These  few  examples  are  sufficient  to  show  the  many-sided  applica- 
tions of  the  above  reaction. 

The  most  remarkable  characteristic  of  acetacetic  ester  is  that  a  portion 
of  its  hydrogen  may  be  substituted  by  metals.  If  sodium  is  allowed  to 
act  on  it,  the  sodium  salt  is  formed  with  the  elimination  of  hydrogen : 

CH3.CO.CHH.CO.OC.,H5  +  Na  =  CH3.CO.CHNa.CO.OC2H5  +  H 

The  same  salt  is  also  formed  by  shaking  the  ester  with  a  solution  of 
sodium  hydroxide.  The  reason  for  this  phenomenon  is  to  be  sought 
in  the  acidifying  influence  of  the  two  neighbouring  carbonyl  (CO) 
groups. 

The  synthetical  importance  of  acetacetic  ester  depends  on  the  fact 
that  the  most  various  organic  halogen  substitution  products  react  with 
sodium  acetacetic  ester,  the  halogen  uniting  with  the  sodium,  with  the 
condensation  of  the  two  remaining  residues.  Thus  a  large  number  of 
compounds  may  be  built  up  from  their  constituents.  A  few  typical 
examples  may  elucidate  these  statements: 

(1)  CH8.CO.CHNa.COOC2H5-f-ICH, 

-  CH3 .  CO .  CH .  CO .  OC2H5  +  Nal 

CH3 

Methylacetacetic  ester 

(2)  CH3 .  CO .  CHNa .  CO .  OC2H3  +  C6H, .  CO .  Cl 

Benzoyl  chloride 

=  CH3 .  CO .  CH  -  CO .  OC2H5  -f  NaCl 
CO 


Benzoylacetacetic  ester 

(3)  CH3.CO.CHNa.COOC2H5  +  Cl.CH2.CO.OC2H5  = 

Chloracetic  ester 

CH3.CO.CH.CO.OC2H5 

CH2  -f-  NaCl. 


COOCo 


Acetsuccinic  ester 


1  84  SPECIAL   PART 

In  the  compounds  thus  obtained  the  second  methylene  hydrogen 
atom  is  also  replaceable  by  sodium,  and  this  salt  is  likewise  capable  of 
entering  into  similar  reactions,  by  which  the  number  of  derivatives  is 
largely  increased,  e.g.  : 

CH3.CO.C.Na-CO.OCoHi  +  IC2ri5  =  CH3.CO.C—  CO.OC,H3+NaI. 
CH3  CH,    C2H. 

Sodiummethylacetacetic  ester  Methylethylacetacetic  ester 

From  all  these  compounds  simpler  ones  may  be  obtained  on  saponi- 
fication.  The  acetacetic  ester  breaks  up  in  one  of  two  ways,  depend- 
ing upon  the  conditions  of  the  saponification  : 


Acetone 

CH3.CO.iCH2.CO.OC2H5  +  2HOH  =  2CH,.CO.OH  +  C2H-.OH. 

:  Acetic  acid 

The  first  kind  of  decomposition  is  called  "ketone  decomposition," 
the  second,  "acid  decomposition.1'  Since,  as  shown  above,  either  one 
or  both  of  the  methylene  hydrogen  atoms  in  acetacetic  ester  can  be 
replaced  by  different  radicals,  X  or  Y,  these  substances  yield  either 
mono-  or  di-  substituted  acetones  : 

X\ 
X.CH..CO.CH.J    and          >CH.CO.CH, 

Y/ 
as  well  as  mono-  and  di-  substituted  acetic  acids, 

X\ 
X.CHn.CO.OH      and          >CH.CO.OH. 

Y/ 

The  variety  of  the  acetacetic  ester  syntheses  is  still  further  increased 
by  the  fact  that  two  molecules  of  the  ester,  by  reaction  with  aldehydes 
or  alkylene  bromides,  may  be  united  with  one  another  by  the  most 
various  bivalent  radicals. 

According  to  recent  researches  of  K.  H.  Meyer1  and  Knorr2  espe- 
cially, the  optical  behaviour  of  ordinary  acetacetic  ester  indicates  that 
it  consists  of  a  mixture  of  the  ketoform  mainly,  with  a  small  quantity 
of  the  enolform  (/3-oxycrotonic  ester),  these  two  being  in  a  state  of 


i  A.  280,  212.  2  B.  44,  1138. 


ALIPHATIC   SERIES  185 

equilibrium.  When  the  mixture  is  cooled  with  solid  carbon  dioxide 
and  ether  to  —  78°,  the  pure  ketoform  crystallises  out.  When  the  dry- 
sodium  salt  of  acetacetic  ester  is  decomposed  at  a  low  temperature  with 
dry  hydrogen  chloride,  pure  enolform  is  obtained  which  does  not 
solidify  at  —  78°.  It  readily  reacts  with  ferric  chloride  and  is  coloured 
red.  The  ketoform  does  not  behave  in  this  manner.  It  is  true  that 
the  latter  may  also  give  the  red  colouration  on  standing  for  a  short  or 
a  longer  period ;  this,  however,  is  due  to  the  enolform  produced  in  the 
reaction  mixture.  The  two  forms  are  converted  one  into  the  other  at 
ordinary  temperatures,  the  final  product  being  the  "equilibrium  acetic 
ester  ".mentioned  above. 

The  sodium  salt  of  acetacetic  ester  is  also  derived,  according  to  its 
optical  behaviour,  from  the  enolform.  The  transpositions  mentioned 
above  are  brought  about  by  the  action  of  methyl  iodide.  A  double 
compound  is  first  formed,  with  a  subsequent  decomposition  into  sodium 
halide. 

(a)  CH3 .  C  =  CH  .  COOC2H5  +  ICH3  =  CH3 .  C— CH  .  COOC2H5 
ONa  ONa  I  CH3 

(J)  CH3 .  C CH  .  COOCoH,  -  CH3 .  CO .  CH  .  COOC2H5  +  Nal 

/\,      I  I 

OJNa  I]    CH3  CH3 


11.   REACTION:    SYNTHESES  OF  THE  HOMOLOGUES  OF  ACETIC  ACID 
BY  MEANS   OF   MALONIC   ESTER 

EXAMPLE  :  Butyric  Acid  from  Acetic  Acid 
(a)   Preparation  of  Malonic  Ester^ 

Dissolve  50  grammes  of  chloracetic  acid  in  100  grammes  of 
water;  warm  gently  (about  50°),  and  neutralise  with  solid,  dry, 
potassium  carbonate,  for  which  30-40  grammes  will  be  required. 
The  solution  is  then  heated  gradually,  with  thorough  stirring,  while 
40  grammes  of  pure,  finely  pulverised  potassium  cyanide  are  added. 
(Use  a  sand-bath  or  asbestos  plate,  under  the  hood.)  The  forma- 


1  A.  204,  121 ;  Journ.  Amer.  Chem.  Soc.  18,  1105. 


1 86  SPECIAL  PART 

tion  of  cyanacetic  acid  takes  place,  with  vigorous  ebullition.  When 
the  reaction  is  complete,  the  mixture  is  evaporated  as  quickly  as 
possible  on  the  sand-bath  until  a  thermometer  placed  in  the  vis- 
cous brownish  salt  indicates  135°.  Since  the  substance  "bumps" 
and  spatters  during  the  evaporation,  it  is  constantly  stirred  with 
the  thermometer,  the  hand  being  protected  by  a  glove  or  cloth. 
It  is  allowed  to  cool,  the  stirring  being  continued  during  the  cool- 
ing, otherwise  the  product  bakes  into  a  hard,  scarcely  pulverisable 
mass.  It  is  then  quickly  powdered  as  finely  as  possible,  placed  in 
a  ^-litre  flask  provided  with  a  reflux  condenser,  and  treated  with 
20  c.c.  of  absolute  alcohol.  A  cooled  mixture  of  80  c.c.  of  absolute 
alcohol  and  80  c.c.  of  concentrated  sulphuric  acid  is  then  added 
gradually,  with  good  shaking,  through  the  condenser  tube.  The 
pasty  mass  is  now  heated,  with  frequent  shaking,  two  hours  in 
a  water-bath  (hood)  ;  it  is  then  well  cooled,  and  treated  with  150 
c.c.  of  water  (shaking).  After  the  undissolved  salt  has  been  filtered 
off  with  suction,  it  is  washed  on  the  filter  several  times  with  ether. 
The  filtrate,  consisting  of  the  water  solution  and  the  ether  wash- 
ings, is  then  carefully  extracted  with  a  sufficiently  large  quantity 
of  ether.  The  ethereal  extract  is  shaken  up  in  a  separating  funnel 
with  a  concentrated  solution  of  sodium  carbonate  until  it  no  longer 
shows  an  acid  reaction.  (  Owing  to  the  copious  evolution  of  gas  the 
funnel  is  not  closed  at  first.)  It  is  then  dried  over  fused  Glauber's 
salt,  and  after  the  evaporation  of  the  ether,  distilled.  Boiling- 
point,  195°.  Yield,  45-50  grammes. 

The  compound  may  also  be  advantageously  dried,  without  the 
use  of  Glauber's  salt,  by  evaporating  off  the  ether,  and  heating 
the  residue  about  a  quarter  hour  in  a  vacuum  on  a  water-bath. 
(Compare  page  55.) 

(b)   The  Introduction  of  an  Ethyl  Group 

Dissolve  2.3  grammes  of  sodium  in  25  grammes  of  absolute 
alcohol  in  a  small  flask  connected  with  a  reflux  condenser ;  treat 
the  cooled  solution  gradually  with  16  grammes  malonic  ester, — 
the  transparent  crystals  of  sodium  ethylate  separating  out  at  first 
pass  over  into  a  voluminous  pasty  mass  of  sodium  malonic  ester,— 


ALIPHATIC  SERIES  1 87 

and  then,  with  shaking,  add  through  the  condenser  20  grammes 
of  ethyl  iodide  in  small  portions.  The  mixture  is  then  heated  on 
the  water-bath  until  the  liquid  no  longer  shows  an  alkaline  reac- 
tion, for  which  one  or  two  hours  may  be  necessary.  The  alcohol 
is  then  distilled  off  on  an  actively  boiling  water-bath,  a  thread  being 
placed  in  the  flask  to  facilitate  the  boiling ;  the  residue  is  taken 
up  with  water  and  extracted  with  ether,  the  ether  evaporated,  and 
the  residue  distilled.  Boiling-point,  206-208°.  Yield,  about  15 
grammes. 

(c)    Saponification  of  Ethyl  Malonic  Ester 

For  the  saponification  of  the  ester,  a  concentrated  solution  of 
caustic  potash  is  prepared ;  for  every  gramme  of  the  ester,  a 
solution  of  1.25  grammes  potassium  hydroxide  in  i  gramme  of 
water  is  used.  The  cooled  solution  is  placed  in  a  flask  provided 
with  a  reflux  condenser  ;  through  this  the  ester  is  gradually  added  ; 
an  emulsion  is  first  formed,  which  soon  solidifies  to  a  white  solid 
mass,  probably  potassium  ethylmalonic  ester.  On  heating  the  mix- 
ture on  a  water-bath  a  sudden  energetic  boiling-up  sets  in,  especially 
if  the  flask  be  shaken.  The  heat  generated  in  the  reaction  causes 
the  alcohol,  liberated  in  the  saponification,  to  boil.  After  about 
an  hour's  heating  on  the  water-bath,  the  oily  layer  disappears, 
showing  that  the  saponification  is  complete. 

The  free  ethyl  malonic  acid  may  be  obtained  by  following  either 
of  the  methods  given  below  : 

(i)  The  solution  is  diluted  with  ii  times  the  volume  of  water 
previously  used  to  dissolve  the  caustic  potash.  To  this  is  added, 
gradually,  with  cooling,  a  quantity  of  concentrated  hydrochloric 
acid  equivalent  to  the  total  amount  of  caustic  potash  used  (the 
strength  of  the  acid  is  determined  by  a  hydrometer).  The  ethyl- 
malonic acid  liberated  is  taken  up  with  not  too  little  ether,  the 
ethereal  solution  dried  over  anhydrous  Glauber's  salt,  the  ether 
evaporated,  and  the  residue  heated,  with  stirring,  on  a  water-bath, 
in  a  large  watch  crystal  or  dish,  until  it  begins  to  solidify.  After 
cooling,  it  is  pressed  out  on  a  drying  plate  and  crystallised  from 
benzene.  Melting-point,  111.5°.  Yield,  about  7  grammes. 


1  88  SPECIAL   PART 

(2)  The  solution  is  diluted  with  the  same  volume  of  water  pie- 
viously  used  to  dissolve  the  caustic  potash.  To  this  is  added 
carefully  and  with  cooling  concentrated  hydrochloric  acid,  until  an 
acid  reaction  may  just  be  detected.  The  ethyl  malonic  acid  is 
precipitated  out  in  the  form  of  its  difficultly  soluble  calcium  salt, 
by  the  addition  of  a  cold  solution  of  calcium  chloride,  as  concen- 
trated as  possible.  This  is  filtered  off,  well  pressed  on  a  porous 
plate,  and  the  ethyl  malonic  acid  liberated  by  treating  carefully 
with  concentrated  hydrochloric  acid  is  obtained  pure  as  in  (  i  )  . 

(d)    Elimination  of  Carbon  Dioxide  from  Ethyl  Malonic  Acid 

The  ethyl  malonic  acid  is  placed  in  a  small  fractionating  flask 
provided  with  a  long  condensing  tube  supported  in  an  oil-bath  at 
an  oblique  angle,  so  that  its  outlet  tube  is  inclined  upward.  The 
mouth  is  closed  by  a  cork  bearing  a  thermometer.  The  acid  is 
heated  at  180°,  until  carbon  dioxide  is  no  longer  evolved,  which 
will  require  about  a  half-hour.  The  residue  is  distilled  from  the 
same  flask  in  the  usual  way  ;  the  butyric  acid  passes  over  between 
162-163°.  Yield,  about  80-90%  of  the  theory. 

(a)  In  the  first  phase  of  the  reaction  which  gives  ethylmalonic  ester, 
the  potassium  cyanide  acts  on  the  chloracetic  acid,  or  on  its  potassium 
salt,  with  the  formation  of  cyanacetic  acid  : 


CH2C1.CO.OH  +  KCN  =  CH2.CN.CO.OH 

Cyanacetic  acid 

As  already  mentioned  in  the  preparation  of  acetonitrile,  a  halogen 
united  with  aliphatic  residues  may  generally  be  replaced  by  the  cyanogen 
group,  on  heating  with  potassium  or  silver  cyanide.  If  alcohol  and 
sulphuric  acid  or  ethylsulphuric  acid  are  now  allowed  to  act  on  the 
cyanacetic  acid,  three  reactions  take  place.  At  first  there  is  an  esterifi- 
-ation  in  accordance  with  the  equation  : 

CH2  .  CN  .  CO  .  OH  +  C2H5  .  OH  =  CH2  .  CN  .  CO  .  OC2H5  +  H2O 

Cyanacetic  ester 

Under  the  discussion  of  acetic  ester,  it  has  already  been  brought 
forward  that,  in  general,  acid  esters  can  be  obtained  by  treating  a  mix- 
ture of  the  alcohol  and  acid  with  sulphuric  acid.  In  the  second  place, 


ALIPHATIC   SERIES  I«9 

the  sulphuric  acid  has  a  saponifying  action  on  the  cyanacetic  ester, 
t.e.j  the  cyanogen  group  is  converted  into  carboxyl  (COOH). 

CO.  OH 

CH2.CN.CO.OC2H5  +  2  H2O  =  CH2  +  NH3  . 

CO.OC2H5 

Acid  ester  of  malonic  acid 

The  carboxy]  group  thus  formed  is  then  acted  on  in  the  same  way 
as  the  carboxyl  group  of  cyanacetic  acid  above,  with  the  formation  of 
an  ester : 

CO.  OH  CO.OC2H5 

H2  +  C9H6.OH  =  CH,  +  H20 

I  I 

CO.OC2H,  CO.OC2H5 

Malonicdiethyl  ester 

{b)  The  ester  of  malonic  acid,  like  acetacetic  ester,  possesses  the 
property  in  virtue  of  which  one  of  the  two  methylene  hydrogen  atoms 
can  be  replaced  by  sodium,  in  consequence  of  the  acid  properties  im- 
parted by  the  two  neighbouring  carbonyl  (CO)  groups.  When  the 
sodium  compound  is  treated  with  organic  halides,  like  alkyl  halides, 
halogen  derivatives  of  acid-esters,  acid-chlorides,  etc.,  the  sodium  is 
replaced  by  alkyl  residues,  acid  residues,  etc.,  just  as  in  the  case  of  the 
closely  related  acetacetic  ester.  In  the  above-mentioned  examples,  the 
sodium  salt  of  the  malonic  ester  is  first  formed  from  sodium  alcoholate 
and  the  ester : 

CO.OCjjH-  CO.OC2H5 


CH  H  +  C2H5.0  Na  =  CHNa          +  C2H5.OH 


CO.OC2H5  CO.OC2H5 

Ethyl  iodide  reacts  on  this  as  follows : 

CO.OC2H5  CO.OC2H5 

CH|Na  +  I|C2H3       =CH.C2H5    -f  Nal 

I  I 

CO.OC2HS  CO.OC2H5 

Ethylmalonicdiethyl  ester 

As  in  acetacetic  ester,  the  second  hydrogen  of  the  malonic  ester  can 
also  be  replaced  by  sodium  ;  cpnsequently  the  malonic  ester  is  capable 


IQO  SPECIAL  PART 

of  reacting  a  second  time  with  organic  halides,  so  that  disubstituted 
malonic  esters  can  also  be  prepared. 

(c)  The  compounds  thus  obtained  of  the  general  formulae : 

CO.OC,H5  CO.OCoH. 

I  !  /x 

CH-X         and    C< 
I  I\Y 

CO.OC2H5  CO.OC2H5 

are  distinguished  from  the  corresponding  derivatives  of  acetacetic  ester 
in  that  on  saponification  they  do  not  decompose,  but  yield  the  free 
substituted  malonic  acids.  Thus,  the  ethylmalonicdiethyl  ester  reacts 
with  caustic  potash  as  follows  : 

CO.OC2H5      KOH      CO.  OK 

CH  .  C2H5  +  =  CH .  C2H5  +  2  C2H5 .  CH 

CO.OC2H,      KOH      CO.  OK 

(d)  From  the  substituted  malonic  acid  thus  obtained,  derivatives 
of  acetic  acid  may  be  prepared  by  heating  it  to  a  high  temperature. 
It  is  a  general  law  that  one  carbon  atom  cannot  hold  two  carboxyl 
groups  in  combination  at  high  temperatures,  since  carbon  dioxide  will 
be  eliminated  from  one.     By  this  means,  a  dicarbonic  acid  is  converted 
into  a  monocarbonic  acid,  e.g. : 

|CO.Q|H 

1  CH3 

CH2  +  CO, 

CO.  OH 
CO.  OH 

From  the  mono-  or  di-  substituted  malonic  acid  a  substituted  acetic 
acid  is  obtained  of  the  formula, 


A, 


CH..X  CH< 

or     |      \Y 

:O.OH       co. OH 

Thus  from  ethylmalonic  acid,  there  is  formed  ethylacetic  acid  = 
butyric  acid.  If,  instead  of  ethyl  iodide,  methyl  or  propyl  iodide 
is  used,  proprionic  acid  or  valerianic  acid  respectively  is  obtained. 
If  two  methyl  groups  are  introduced  into  malonic  ester,  then,  on 
decomposition,  a  dimethylacetic  or  isobutyric  acid  will  be  formed. 

As  shown  above,  similar  acids  may  be  prepared  from  the  acetacetic 
ester.  Since  the  decomposition  of  the  acetacetic  ester  derivatives  may 
take  place  in  two  different  ways  (acid-  and  ketone-decomposition)  ; 


ALIPHATIC  SERIES  igi 

and  since  these  decompositions  frequently  take  place  side  by  side,  while 
the  malonic  acid  derivatives  decompose  in  only  one  way,  so  in  most 
cases  it  is  more  advantageous  to  use  the  malonic  ester  for  the  synthesis 
of  the  homologous  fatty  acids. 


12.  REACTION:  PREPARATION  OF  A  HYDROCARBON  OF  THE 
ETHYLENE  SERIES  BY  THE  ELIMINATION  OF  WATER  FROM  AN 
ALCOHOL.  COMBINATION  OF  THE  HYDROCARBON  WITH  BROMINE 

EXAMPLE  :  Ethylene  from  Ethyl  Alcohol.     Ethylene  Bromide 1 

(a)    From  Ethyl  Alcohol  and  Sulphuric  Acid 

A  mixture  of  25  grammes  of  alcohol,  150  grammes  of  concen- 
trated sulphuric  acid,  and  30  grammes  of  coarse-grained  sea-sand 
(freed  from  fine  particles)  is  heated,  not  too  strongly,  in  a  litre 
round  flask  on  a  sand-bath  or  a  wire  gauze  covered  with  thin 
asbestos  paper.  As  soon  as  an  active  evolution  of  ethylene  takes 
place,  add,  through  a  dropping  funnel,  a  mixture  of  i  part  alcohol 
and  2  parts  concentrated  sulphuric  acid  (made  by  pouring  150 
grammes  of  alcohol  into  300  grammes  of  sulphuric  acid,  with  con- 
stant stirring),  slowly,  so  that  a  regular  stream  of  gas  is  evolved. 
If  the  mixture  in  the  flask  foams  badly  with  a  separation  of  car- 
bon, it  has  been  too  strongly  heated,  and  it  is  advisable  to  empty 
the  flask  and  begin  the  operation  anew  with  a.  smaller  flame.  In 
order  to  free  the  ethylene  from  alcohol,  ether,  and  sulphur  dioxide, 
it  is  passed  through  a  wash-bottle  containing  sulphuric  acid,  and  a 
second  one,  provided  with  three  tubulures,  the  central  one  sup- 
plied with  a  -safety-tube,  containing  a  dilute  solution  of  caustic 
soda.  It  then  enters  two  wash-bottles,  each  containing  25  c.c.  of 
bromine,  covered  with  a  layer  of  water  i  cm.  high.  Since  the 
combination  of  ethylene  with  bromine  causes  the  evolution  of  heat, 
the  bromine  bottles  are  placed  in  thick-walled  vessels  filled 
with  cold  water.  In  order  to  get  rid  of  the  bromine  vapours 
which  escape  from  the  last  bottle,  it  is  connected  with  the  hood 
or  with  a  flask  containing  a  solution  of  caustic  soda ;  to  prevent  the 

1  A.  168,  64;  A.  192,  244. 


IQ2  SPECIAL  PART 

caustic  soda  from  being  drawn  back  into  the  bromine  bottle,  the 
delivery  tube  must  not  dip  under  the  surface  of  the  caustic  soda, 
and  the  stopper  must  be  provided  with  canals  cut  in  the  sides. 
As  soon  as  the  bromine  is  decolourised,  which  requires  4-5 
hours  under  normal  conditions,  the  operation  is  discontinued, 
care  being  taken  to  disconnect  all  of  the  vessels  immediately; 


t 

FIG.  67. 

otherwise,  in  consequence  of  the  cooling  of  the  large  flask,  the 
contents  of  the  bottles  will  be  drawn  back.  The  ethylene  bromide 
is  then  washed  repeatedly  with  water  in  a  dropping  funnel,  and, 
finally,  with  caustic  soda  solution.  It  is  dried  over  calcium 
chloride,  and,  on  distillation,  is  obtained  perfectly  pure.  Boiling- 
point,  130°.  Yield,  125-150  grammes. 

The  addition  of  the  alcohol-sulphuric  acid  mixture  is  often  at- 
tended with  difficulty,  in  that  as  soon  as  the  cock  is  opened,  the  gas 
passes  out  through  the  funnel,  thus  preventing  the  entrance  of  the 
mixture.  This  difficulty  may  be  obviated  by  taking  the  precaution 
of  always  keeping  the  stem  of  the  funnel  filled  with  the  mixture. 
Before  the  heating  is  begun,  a  portion  of  the  mixture  is  placed  in 
a  porcelain  dish,  the  end  of  the  stem  of  the  funnel  immersed 
in  it  and  filled  by  suction.  The  cock  is  then  closed,  the  funnel 
placed  in  the  cork  of  the  generating  flask,  and  the  heating 
begun. 


ALIPHATIC   SERIES  1 93 

(fr)  From  Ethyl  Alcohol  and  Phosphoric  Acid 

Separation  of  carbon  and  foaming  will  be  prevented  in  the 
preparation  of  ethylene  when  syrupy  phosphoric  acid  is  used  in 
place  of  sulphuric  acid.  A  200  c.c.  round  flask,  with  a  wide  mouth, 
is  provided  with  a  three-hole  cork.  Through  one  hole  passes  a 
thermometer  extending  to  the  bottom  of  the  flask,  through  the 
second  hole  is  inserted  a  dropping  funnel ;  the  stem  of  the  latter 
is  at  least  25  cm.  long  and  is  drawn  to  a  fine  point.  The  end  of 
the  stem  is  kept  only  a  few  millimetres  below  the  stopper.  Through 
the  third  hole  passes  a  delivery  tube,  not  too  narrow,  bent  at  right 
angles.  The  tube  is  attached  with  rubber  to  a  Wolfe  flask,  pro- 
vided with  two  tubulures  flush  with  the  stoppers.  The  flask  is 
completely  surrounded  with  broken  ice.  Then  follow  two  wash- 
bottles  surrounded  with  ice  for  bromine,  and  finally  a  flask  con- 
taining a  solution  of  sodium  hydroxide,  as  in  method  (a).  For 
the  preparation  of  ethylene  120  grammes  of  syrupy  phosphoric 
acid,  sp,  gr.  1.7-1.75,  are  placed  in  an  open  vessel  and  gradually 
heated.  The  acid  is  stirred  with  a  thermometer.  At  160°  water 
begins  to  be  given  off.  The  heating  is  continued,  until  at  220°  the 
evolution  of  vapour  is  very  slight.  The  acid  is  somewhat  cooled 
and  poured  into  the  flask.  It  is  heated  to  210-220°  over  an 
asbestos  gauze  ;  at  this  temperature  ordinary  alcohol  is  allowed  to 
run  into  the  flask,  drop  by  drop,  from  the  funnel,  the  steam  of 
which  should  have  been  previously  filled  with  alcohol,  as  in  method 
(a).  A  steady  current  of  ethylene  is  thus  evolved.  The  decolouri- 
sation  of  bromine  requires  3^-4-9-  hours.  The  crude  product  is 
purified  as  in  method  (a). 

The  hydrocarbons  of  the  ethylene  series  may  be  prepared,  in  general, 
by  abstracting  water  from  the  corresponding  alcohol,  e.g. : 

CH3 .  CH2 .  OH  =  CH2=CH2  +  H2O 

If  sulphuric  acid  or  phosphoric  acid  is  used  as  the  dehydrating  agent, 
the  reaction  does  not  follow  the  above  equation,  but  ethylsulphuric  acid 
or  ethylphosphoric  acid  is  first  formed,  and  this,  on  heating,  yields  sul- 
phuric acid  or  phosphoric  acid. 


SPECIAL  PART 


C2H5  .  OH  +  S02      =  S02  +  H2O 

X)H        X>H 

Ethylsulphuric  add 

X)C2H5  X)H 

$02  =  C2H4  +  S02     . 

NOH  NDH 

In  many  cases  the  elimination  of  water  takes  place  so  easily  that 
the  use  of  concentrated  sulphuric  acid  is  unnecessary,  since  the  diluted 
acid  answers  the  purpose.  With  the  higher  members  of  the  series  the 
reaction  is  complicated  by  the  fact  that  the  simple  alkylenes  polymerise 
under  the  influence  of  sulphuric  acid.  Thus  there  is  formed,  besides 
butylene,  C4H8,  hydrocarbons  having  respectively  twice  and  three  times 
its  molecular  weight,  e.g.  : 

C8H16  Dibutylene 

C12H24  Tributylene 

In  these  cases  it  is  much  more  convenient  to  prepare  an  ester  from 
the  alcohol  by  the  action  of  the  chloride  of  a  higher  fatty  acid,  and 
subjecting  this  to  distillation  by  which  it  is  decomposed  into  an  hydro- 
carbon of  the  ethylene  series  and  the  free  fatty  acid,  e.g.  : 

C15H31.CO.OC16H33  -  C14H.r  CO.OH  4-  C16H32 

Cetyl  palmitate  Palmitic  acid        Hexadecylene 

The  first  four  members  of  the  alkylene  series  are  gases  at  ordinary 
temperatures,  which  burn  with  strongly  luminous,  smoky  flames.  The 
intermediate  members  are  colourless  liquids,  not  miscible  with  water, 
which  can  be  distilled  at  ordinary  pressures  without  decomposition; 
the  higher  members  are  solids,  and  can  only  be  distilled  without  de- 
composition in  a  vacuum.  Chemically  these  compounds  are  charac- 
terised primarily  by  the  property  of  uniting  with  two  univalent  atoms, 
or  a  univalent  atom  and  a  univalent  radical,  upon  which  the  double 
union  is  changed  to  single  union. 

They  take  up,  especially  in  the  presence  of  platinum-black,  two 
atoms  of  hydrogen,  thus  passing  over  to  the  hydrocarbons  of  the  satu- 
rated series  (paraffins)  : 

CH,=CH,  +  H9  =  CH»  -  CH«. 


ALIPHATIC   SERIES  1 95 

Hydrogen  halides  may  also  be  added  to  them ;  hydriodic  acid  with 
the  greatest  ease,  hydrobromic  acid  with  less,  and  hydrochloric  acid 
only  with  difficulty : 

CH^CH,  +  HI  =  CH3.CH2I. 

Ethyl  iodide 

The  homologues  of  ethylene  also  form  addition  products ;  the  halo- 
gen atom  seeks  that  carbon  atom  which  is  combined  with  the  smallest 
number  of  hydrogen  atoms  : 

CH2=CH .  CH3  +  HI  =  CH3 .  CHI .  CH3 . 

Propylene  Isopropyl  iodide 

The  constituents  of  water  (H  and  OH)  may  also  be  added  indirectly 
to  the  alkylenes.  If  concentrated  sulphuric  acid  be  allowed  to  act  on 
one  of  them,  it  dissolves,  forming  a  sulphuric  acid  ester : 

/OH         X)C2H5 
CHgzrCH,  +  S02       -  S02          , 
\DH       \DH 

If  this  is  boiled  with  water,  the  ester  is  decomposed  into  alcohol  and 
sulphuric  acid : 

//OC2H5 

SO2  -fHOH     =  C2H5.OH 

X)H  X)H 

so  that  finally  H  and  OH  have  been  added  to  ethylene : 
CH^CH,  H-  H.OH  -  CH3.CH2.OH. 

Analogous  to  the  halogen  atoms,  the  hydroxyl  (OH)  group  unites 
with  that  carbon  atom  holding  in  combination  the  smallest  number  of 
hydrogen  atoms. 

The  alkylenes  take  up  two  atoms  of  chlorine  or  bromine  with  great 
ease: 

CH2=CH2  +  C12  =  CH2C1  -  CH2C1 

CH2=CH2  +  Br2  =  CH2Br  -  CH2Br. 

Finally  they  combine  directly  with  hypochlorous  acid  to  form  glycol- 
chlorhydrines. 

The  reactions  taking  place  in  the  formation  of  the  alkylenes  as  well 
as  those  in  the  formation  of  addition  products  are  not  only  applicable 


196  SPECIAL  PART 

to  the  hydrocarbons  but  also  to  their  substitution  products.  Thus, 
e.g.,  unsaturated  acids  are  commonly  obtained  from  oxyacids  by  the 
elimination  of  water : 

CH2.OH.CH2.CO.OH  =  CH2=CH.CO.OH  +  H2O 

/3-hydroxypropionic  acid  Acrylic  acid 

C6H5 .  CH .  OH .  CH2 .  CO .  OH         =  C6H5 .  CHzzCH .  CO .  OH  +  H2O 

Phenyllactic  acid  Cinnamic  acid 

All  compounds  in  which  the  ethylene  condition  is  present  show  the 
addition  phenomena,  in  accordance  with  the  following  equations : 

CH2— CH.CH2.OH  +  Br2  =  CH2Br  -  CHBr.CH2.OH 

Allyl  alcohol  Dibromhydrine 

CH2=CH .  CO .  OH  +  Br2  =  CH2Br  -  CHBr .  CO .  OH 

Acrylic  acid  Dibrompropionic  acid 

C6H5.CH=CH.CO.OH  +  Br2       =  C6H5.CHBr  -  CHBr.  CO. OH 

Cinnamic  acid  Dibromhydrocinnamic  acid 

C6H5.CHziCH.CO.OH  +  HBr      =  C6H5.CHBr  -  CH2.CO  .OH 

Bromhydrocinnamic  acid 

C6H5 . CH=CH2  +  Br2  =  C6H5 .CHBr  -  CH2Br, 

Styrene  Styrene  dibromide 

C6H5.CH=CH.CO.OH4  C1.OH=C6H5.CH.OH.CHC1.CO.OH 

Phenylchlorlactic  acid 

CH2— CH.CO.OH  +  H3  =  CH3.CH2.CO.OH. 

Acrylic  acid  Propionic  acid 


13.  REACTION:  REPLACEMENT  OP  HALOGEN  ATOMS  BY  ALCOHOLIC 
HYDROXYL  GROUPS 

EXAMPLE  :  Ethylene  Alcohol  (Glycol)  from  Ethylene  Bromide 
(a)   Conversion  of  Ethylene  Bromide  into  Glycoldiacetate 

A  mixture  of  60  grammes  ethylene  bromide,  20  grammes  glacial 
acetic  acid,  and  60  grammes  of  freshly  fused,  finely  pulverised 


ALIPHATIC  SERIES  197 

potassium  acetate,1  placed  in  a  i-litre,  short-necked,  round  ft>sk, 
provided  with  a  reflux  condenser,  is  heated  to  active  boiling  for 
two  hours  on  a  sand-bath  over  a  large  flame.  The  reaction  prod- 
uct is  then  distilled  (with  a  condenser)  over  a  large  luminous 
flame  kept  in  continuous  motion.  Toward  the  end  of  the  distilla- 
tion the  flame  is  gradually  made  non-luminous.  The  distillate  is 
then  further  treated  with  60  grammes  ethylene  bromide  and  80 
grammes  potassium  acetate,  and  the  mixture,  as  above,  heated  to 
active  boiling  for  two  to  three  hours  on  a  sand-bath.  The  re- 
action product  is  then  again  distilled  over  (with  a  condenser)  by 
a  luminous  flame.  The  distillate  is  fractioned  —  using  a  10  cm. 
long  Hempel  tube.  The  fractions  are  collected  as  follows  :  i.  up 
to  140°;  2.  from  140-175°;  3.  above  175°.  Fractions  2  and  3 
are  then  again  distilled  separately.  The  pure  glycoldiacetate 
goes  over  between  180-190°,  the  main  portion  at  186°.  Yield, 
about  70  grammes. 

If  it  is  desired  to  increase  the  yield,  the  portion  going  over 
under  180°  is  heated  for  three  hours  longer  with  potassium  acetate. 
The  product  is  then  treated  as  above  described.  This  causes  an 
increase  of  about  15  grammes. 


(fr)  Saponification  of  Glycoldiacetate* 

Glycoldiacetate  is  saponified  by  heating  with  a  solution  of  hydro- 
chloric acid  in  methyl  alcohol.  For  this  purpose  a  mixture  of 
100  grammes  ordinary  methyl  alcohol  and  a  quantity  of  compact 
slaked  lime  (about  one-third  of  the  alcoholic  volume)  is  heated 
for  several  hours  on  a  water-bath  to  active  boiling,  in  a  flask  at- 


1  Potassium  acetate  (Kalium  aceticum  pur.  Ph.  G.  III.),  differing  from  sodium 
acetate  (compare  page  147),  crystallises  without  water  of  crystallisation.     Never- 
theless, for  this  experiment  it  must  be  heated  to  fusion  over  a  free  flame  in  an  iron 
or  nickel  dish.     The  melted  salt  is  poured  into  a  shallow,  flat  iron  or  copper  dish, 
in  a  thin  layer.     While  still  warm  it  is  pulverised  as  finely  as  possible,  and  must  be 
at  once  transferred  to  a  bottle  which  is  to  be  kept  tightly  closed.     For  this  experi- 
ment 200  grammes  of  the  salt  are  fused. 

2  A  private  method;  by  courtesy  of  Prof.  Henry  (Lowen). 


1 98  SPECIAL  PART 

tached  to  a  reflux  condenser.  The  dehydrated  methyl  alcohol  is 
now  distilled.  It  is  then  subjected  to  fractional  distillation,  and 
the  portion  distilling  at  66-67°  *s  collected  separately.  44 
grammes  of  pure  methyl  alcohol  are  weighed  in  a  small  flask  tared 
with  its  delivery  tube.  Gaseous  hydrochloric  acid  is  now  passed 
into  the  alcohol  with  cooling  under  water,  until  a  gain  of  i.i 
grammes  is  obtained.  Should  the  increase  in  weight  be  more  than 
this,  a  calculated  quantity  of  pure  methyl  alcohol  is  added  in  order 
to  obtain  a  2\  %  alcoholic  solution  of  hydrochloric  acid,  which  is 
the  necessary  strength. 

In  a  flask,  provided  with  a  reflux  condenser,  45.1  grammes  of 
the  alcoholic  solution  of  hydrochloric  acid,  and  50  grammes  of 
glycoldiacetate  are  heated  on  an  actively  boiling  water-bath  for 
half  an  hour.  The  reaction  mixture  is  then  quickly  distilled  from 
a  water-bath  with  frequent  shaking ;  methyl  alcohol  and  methyl 
acetate  will  thus  distil  over,  while  glycol  will  remain  in  the  flask 
with  a  small  quantity  of  unsaponified  ester.  These  cannot  be 
separated  from  one  another  by  distillation,  as  their  boiling  points 
are  close  together.  But  the  thick  liquid  in  the  flask  is  shaken  twice 
with  an  equal  volume  of  dry  ether,  whereby  glycoldiacetate  is  taken 
up,  while  glycol  remains  undissolved.  The  ethereal  layer  is  re- 
moved, either  by  decantation,  or  by  the  use  of  a  pipette.  The  gly- 
col is  then  poured  into  a  small  fractionating  flask  connected  with  a 
long  condenser.  During  the  distillation  (heat  slowly  at  first)  a  low- 
boiling  fraction  (to  100°)  is  first  obtained,  when  the  thermometer 
rises  rapidly  to  190°.  The  main  portion  of  glycol  distils  over  at 
195°.  Yield  about  80-90%  of  the  theory  (17-19  grammes). 

This  preparation  shows  a  method  for  replacing  a  halogen  atom  by 
an  alcoholic  hydroxyl  group.  In  Reaction  i  the  reverse  replacement 
was  brought  about,  —  the  substitution  of  a  hydroxyl  group  by  a  halogen. 
This  method  is  obviously  only  of  importance  in  those  cases  in  which  it 
is  more  convenient  to  obtain  the  halogen  derivative  than  the  alco- 
hol. Among  the  monacid  alcohols  it  is  of  value  for  preparing 
isopropyl  alcohol,  normal  secondary  butyl,  and  normal  secondary  hexyl 
alcoholso 


ALIPHATIC  SERIES  1 99 

As  stated  on  page  135,  the  action  of  hydriodic  acid  on  polyacid  alco- 
hols does  not  yield,  as  might  be  expected,  the  poly-iodine  derivatives, 
but  mono-iodine  derivatives.  Thus  from  glycerol,  isopropyl  iodide  is 
obtained ;  from  erythrite,  normal  secondary  butyl  iodide ;  from  man- 
nite,  the  normal  secondary  hexyl  iodide.  These  iodides,  as  pointed 
out,  may  be  converted  into  the  corresponding  alcohols.  The  method 
is  of  practical  value  in  the  preparation  of  tertiary  alcohols  from  acid- 
chlorides  and  zinc  alkyls.  —  Butlerow^s  synthesis.  Compare  page  146. 
In  this  reaction  the  tertiary  chloride  is  formed  as  an  intermediate 
product.  The  method  is  of  importance  for  the  preparation  of  di-acid 
alcohols  (glycols),  especially  for  the  a-glycols,  in  which  the  hydroxyl 
groups  are  combined  with  the  two  adjacent  carbon  atoms.  The 
dibromides  corresponding  to  these  alcohols  are  easily  obtained  by  the 
.  addition  of  bromine  to  the  hydrocarbons  of  the  ethylene  series.  In 
this  way  glycol  was  first  prepared  by  Wurtz.1 

Other  glycols  may  be  obtained  in  a  similar  manner,  e.g.,  if  allyl 
bromide  be  treated  with  hydrobromic  acid,  trimethylene  bromide  is 
formed,  from  which  a  /?-glycol —  trimethylene  glycol  —  may  be  obtained 
by  the  above  reaction. 

If,  to  unsaturated  mono-acid  alcohols  containing  a  double  union,  two 
bromine  atoms  be  added,  dibrom-alcohols  are  obtained  which,  by  re- 
placing the  bromine  with  hydroxyl,  yield  tri-acid  alcohols : 

H2=:CH.CH2Br  +  BrH  =  CH2Br.CH2.CH2Br  — >-  CH2(OH) .CH2.CH2(OH) 

Allyl  bromide  Trimethylene  bromide  Trimethylene  glycol 


CH3  CH3  CH3 

H  CHBr  CH(OH) 

+  Br2  =  |         -^       | 
H  CHBr  CH(OH) 

I  I  I 

CH2(OH)     CH2(OH)     CH,(OH) 

From  these  examples  the  value  of  this  method  for  obtaining  alcohols  is 
evident. 

Oxyaldehydes,  oxyketones,  and  oxyacids  may  also  be  obtained  by  this 
reaction,  from  the  corresponding  halogen  compounds.  Finally,  it  may 
be  employed  to  replace  the  halogen,  in  side-chains  of  aromatic  com- 
pounds, by  hydroxyl. 

The  substitution  of  halogen  atoms  by  hydroxyl  groups  may  be  done 

1A.  ch.  (3),  55,  400. 


200  SPECIAL   PART 

by  two  methods:  (i)  Directly  in  a  single  operation.  (2)  In  two  re- 
actions ;  (a)  by  preparing  an  acid-ester  of  the  desired  alcohol,  and 
(b)  subjecting  this  to  saponification.  If  method  (i )  be  used,  the  halogen 
derivative  is  heated  with  water  at  the  ordinary  pressure,  or  if  necessary, 
at  an  increased  pressure.  The  same  object  is  attained  more  quickly, 
and  in  many  cases  with  a  better  yield,  by  the  addition  to  the  reaction- 
mixture  of  certain  oxides,  hydroxides,  or  carbonates.  Silver  oxide,  lead 
hydroxide,  barium  hydroxide,  potassium  or  sodium  carbonate,  and  others 
may  be  used  for  this  purpose.  It  appears  to  be  true  that  a  tertiary 
halogen  atom  reacts  more  easily  than  a  secondary  or  primary,  and  that 
a  secondary,  more  easily  than  a  primary.  By  following  this  method, 
glycol  may  be  obtained  .directly  from  ethylene  bromide,  if  the  latter  be 
heated  with  water  and  potassium  carbonate : 

CH.Br  CH.,(OH) 

4-  K2CO3  +  H9O  =|  +  CO2  +  2  KBr 

CH2Br  CH2(OH) 

The  separation  of  the  glycol  from  the  large  excess  of  water  used  is 
troublesome. 

In  accordance  with  method  (2)  certain  salts,  as  silver,  potassium,  or 
sodium  acetate  are  allowed  to  act  on  the  halogen  substitution  product. 
This  results  in  the  formation  of  an  ester  of  the  desired  alcohol : 

CH2Br  CH.,.OOC.CH3 

|  +2CH3.COOK  =  |  '  +2  KBr 

CH2Br  CH2.OOC.CH, 

Glycoldiacetate 

The  ester  is  then  saponified  under  the  proper  conditions,  upon  which 
the  free  alcohol  is  obtained : 

CH2.OOC.CH3  CH2(OH) 

+  2HC1=    I  +2CH8.CO.C1. 

CH2.OOC.CH3  CH2(OH) 

The  acetyl  chloride  reacts  with  methyl  alcohol  forming  methyl  acetate 
with  the  liberation  of  a  fresh  quantity  of  hydrochloric  acid.  Glycol  is  a 
thick,  colourless,  odourless  liquid,  boiling  at  195°;  it  melts  at  11.5°  after 
having  been  solidified  by  low  temperature.  Like  all  poly-acid  alcohols, 
it  has  a  sweet  taste.  It  is  easily  soluble  in  water  and  in  alcohol,  but  not 
in  ether.  Chemically  it  differs  only  from  the  mono-acid  alcohols  in  its 
ability  to  form  mono-  or  di-  derivatives  according  to  the  conditions : 

CH2.ONa        CH2.ONa     CH,.OOC.CH3        CH,.OOC.CH3 

and  |  »     |_  •  and  I 

CH2.OH  CHa.ONa     CH2.OH  CH2.OOC.CH3 


ALIPHATIC   SERIES  2OI 

Both  hydroxyl  groups  are  replaced  by  the  action  of  phosphorus  penta 
chloride : 

CH2(OH)  CH2.C1 

|  +  2  PC15  =  |  +2  POC13  +  2  HC1 

CH. 


But  if  glycol  be  heated  with  hydrochloric  acid,  only  one  hydroxyl  group 
is  replaced : 

CH,(OH)  CH2.C1 

|  +  HC1  =  |  +  H20 

CH2(OH)  CH2(OH) 

Ethylene  chlorhydrine 

From  these  so-called  halogen  hydrines,  by  the  action  of  alkalies  the 
inner  anhydrides  of  the  glycols  are  obtained : 

CH9.C1  O 

|  =  I 

CH2.(OH)      CH 

Ethylene  oxide 


202  SPECIAL   PART 


TRANSITION   FROM   THE   ALIPHATIC   TO   THE 
AROMATIC    SERIES 

Dimethylcyclohexenone  and  s-Xylenol  from  Ethylidenebisacetacetic 
Ester.  (Ring  Closing  in  a  1.5  Diketone.  Knoevenagel  Reaction.1) 

1.  ETHYLIDENEBISACETACETIC  ESTER 

In  a  thick-walled  flask  closed  by  a  cork  bearing  a  thermometer 
reaching  almost  to  the  bottom,  treat  50  grammes  of  pure  (in  vac- 
uum distilled),  cooled  acetacetic  ester  with  8.5  grammes  of  pure 
aldehyde  distilled  just  before  the  experiment.  The  flask  is  cooled 
to  —  10-15°  in  a  freezing  mixture  of  ice  and  salt.  To  the  reac- 
tion-mixture is  then  added  a  few  drops  of  diethyl  amine  from  a 
small  medicine  "  dropper."  In  most  cases  no  elevation  of  tem- 
perature takes  place  at  first.  Since  it  is  very  difficult  to  obtain 
acetacetic  ester  and  aldehyde  absolutely  free  from  acids,  the  first 
portions  of  the  amine  are  neutralised  by  the  acids  present,  and  are 
thus  not  available  for  the  main  reaction.  The  addition  of  the 
amine  is  continued  slowly  until  at  a  certain  point  an  elevation  of  a 
few  degrees  in  the  temperature  is  observed.  Normally  this  should 
occur  on  the  addition  of  the  first  ten  drops.  When  this  takes 
place,  the  liquid,  clear  at  first,  becomes  turbid.  From  this  point, 
during  the  gradual  addition  of  a  further  portion  of  ten  drops  of  the 
base,  the  temperature  is  slowly  allowed  to  rise  to  o°.  The  addi- 
tion of  the  base  in  drops  is  continued,  gradually  and  with  frequent 
shaking,  until,  collectively,  60  drops  =  1.5  grammes  have  been 
used.  The  length  of  the  operation  is  about  an  hour.  After  the 
reaction-mixture  has  stood  a  further  quarter  hour,  it  is  removed 
from  the  freezing  mixture  and  allowed  to  come  to  the  room  tem- 
perature. If,  in  consequence  of  a  secondary  reaction,  the  temper- 

i  A.  281, 25. 


TRANSITION  FROM  ALIPHATIC  TO  AROMATIC  SERIES      2O3 

ature  should  go  up  to  20°,  the  flask  is  cooled  off  a  short  time  in 
ice  water.  The  reaction-product  is  a  viscous,  bright  yellow  liquid 
in  which  numerous  drops  of  water  are  suspended.  It  is  allowed 
to  stand  undisturbed  until  it  solidifies  to  a  crystalline  mass,  which 
generally  requires  from  two  to  three  days. 

A  small  specimen  is  pressed  out  on  a  porous  plate  and  recrystal- 
lised  from  diluted  alcohol.  Colourless  needles  are  thus  obtained 
which  melt  at  79-80°.  Concerning  the  constitution  of  this  sub- 
stance see  the  remarks  on  page  207. 

The  solidification  of  the  crude  product  may  be  hastened  by 
seeding  it,  after  one  day's  standing,  with  crystals  obtained  in  a 
previous  preparation.  This  is  best  done  on  the  upper  portion 
of  the  flask,  which  is  only  moistened  by  the  liquid. 

2.   DIMETHYLCYCLOHEXENONE 

The  crude  product  liquefied  by  heating  in  a  water-bath  is  poured 
into  a  mixture  of  400  grammes  of  water  and  100  grammes  of  con- 
centrated sulphuric  acid  contained  in  a  round  litre  flask  provided 
with  a  long  reflux  condenser.  The  reaction-mixture  is  heated  to 
lively  boiling  on  a  wire  gauze ;  a  few  pieces  of  unglazed  porcelain 
are  placed  in  the  flask  to  insure  a  regular  ebullition. 

After  about  seven  hours'  heating  (the  experiment  should  be 
commenced  in  the  morning  of  a  working-day),  the  reflux  con- 
denser is  replaced  by  an  ordinary  condenser,  and  steam  is  passed 
into  the  mixture  until  the  distillate  measures  about  100  c.c.  The 
flask  is  heated  by  a  free  flame  up  to  the  boiling-point  of  its  con- 
tents. The  distillate  is  preserved  in  a  well-closed  vessel. 

On  the  second  day  the  mixture  is  again  heated  for  seven  hours 
(with  a  reflux  condenser,  new  porcelain  scraps  in  the  flask),  and 
then  100  c.c.  are  again  distilled  off  with  steam.  This  is  repeated 
on  the  third  day,  and  finally  stearn  is  passed  into  the  mixture  until 
from  a  test  portion  of  the  distillate  saturated  with  solid  potash  no 
oil,  or  only  a  minute  quantity,  separates  out.  The  three  distillates 
in  which  the  reaction-product  is  for  the  most  part  dissolved  are 
now  united.  Solid  potash  is  added  until  it  is  no  longer  dissolved. 

For  the  success  of  the  salting  out,  one  must  use  anhydrous  potash 


204  SPECIAL  PART 

as  pure  as  possible.  From  the  potash  solution  a  brownish  red  oily 
layer  separates  out :  it  consists  of  dimethylcyclohexenone  and 
alcohol.  It  is  separated  from  the  water  solution  m  a  dropping 
funnel,  and  the  alcohol  is  distilled  off  by  the  aid  of  a  Hempel  tube 
10  cm.  long  rilled  with  glass  beads.  The  residue  is  dried  over 
fused  Glauber's  salt  and  distilled  from  an  ordinary  fractionating 
flask.  The  portion  going  over  between  200-215°  ^s  collected 
separately.  Boiling-point  of  the  pure  compound,  211°.  Yield, 
15-20  grammes. 

3.   s-XYLENOL 

A  mixture,  cooled  by  ice  water,  of  10  grammes  of  the  ketone 
dissolved  in  20  grammes  of  glacial  acetic  acid  (the  acid  must  not 
be  allowed  to  solidify)  is  treated  gradually  with  a  mixture  of  13 
grammes  of  bromine  and  10  grammes  of  glacial  acetic  acid  from 
a  dropping  funnel.  The  reaction-mixture  is  then  allowed  to  stand, 
under  the  liood,  at  least  half  a  day,  or  better  over  night,  at  the 
room  temperature.  Hydrobromic  acid  is  evolved  copiously.  The 
mixture  is  heated,  with  frequent  shaking,  about  an  hour  on  a  water- 
bath  to  about  50°,  the  temperature  is  then  increased  until  the 
water  boils,  and  the  heating  is  continued  until  there  is  only  a 
slight  evolution  of  hydrobromic  acid.  It  is  heated  finally,  using 
an  air  condenser,  on  a  wire  gauze,  to  incipient  ebullition  of  the 
acetic  acid,  until  the  evolution  of  hydrobromic  acid  almost  entirely 
ceases.  After  cooling,  it  is  poured  carefully  into  a  cooled  solution 
of  75  grammes  of  caustic  potash  in  150  grammes  of  water,  upon 
which  only  a  small  quantity  of  an  oil  should  separate  out.  The 
by-products  insoluble  in  the  alkaline  solution  are  extracted  with  a 
sufficient  quantity  of  ether,  the  alkaline  solution  is  saturated  with 
carbon  dioxide,  and  the  s-xylenol  liberated  is  distilled  over  in  the 
presence  of  carbon  dioxide  with  steam  (use  a  three-hole  cork). 
The  end  of  the  distillation  may  be  readily  determined.  So  long 
as  the  xylenol  is  coming  over,  a  test  of  the  distillate  by  adding  a 
few  drops  of  bromine  will  show  a  precipitate  of  tribromxylenol. 

If  the  distillate  be  allowed  to  stand  in  a  cool  place  over  night, 


TRANSITION  FROM  ALIPHATIC  TO  AROMATIC  SERIES      2O5 

the  larger  portion  of  the  xylenol  will  crystallise  out.  In  order  to 
obtain  the  portion  remaining  dissolved,  the  crystals  are  filtered  off, 
and  the  filtrate  saturated  with  solid  salt  and  extracted  with  ether. 
Melting-point  of  s-xylenol,  64°.  Boiling-point,  220-221°.  Yield, 
5-6  grammes. 

A  better  characterisation  of  this  phenol  is  obtained  by  covering 
a  few  drops  of  it  in  a  test-tube  with  5  c.c.  of  water  and  then  adding 
bromine  drop  by  drop  until  the  reddish  brown  colour  of  the  latter 
does  not  disappear.  The  excess  of  bromine  is  removed  by  the 
addition  of  a  solution  of  sulphur  dioxide.  The  precipitate  is 
recrystallised  from  alcohol.  There  are  thus  obtained  colourless 
needles  of  tribromxylenol,  which  melt  at  165°. 

i.  Aldehydes  unite,  with  the  elimination  of  water,  with  compounds 
containing  the  group  CH2  between  two  negative  radicals  (acetacetic 
ester,  malonic  ester,  acetylacetone,  and  others),  in  two  ways.  i.  Equal 
molecules  unite  in  accordance  with  the  following  equation : 


CH.R 


Example 


CH3  CH, 

CO  CO 


HC.CH3  =  H2O  +  C  =  CH  .CH3 


I 
C 


COOC2H,  COOC2H5 

Ethylideneacetacetic  ester 

2.    The  reaction  may  take  place  between  one  molecule  of  the  alde- 
hyde and  two  molecules  of  the  other  compound  : 

R        X 
CH  -  CH  -  CH 


206  SPECIAL  PART 

Example,  carried  out  in  practice: 


CH3  CH3  CH3  CH3 

CO  CH3  CO  CO      CH3    CO 

CH[Hl  +  CH|0  +  H|CH  =  H2O  +  CH  -  CH  -  CH 
COOC2H5  COOC2K5       COOC2H5     COOC2H5 


a^tic  ester. 


For  bringing  about  the  first  reaction  the  following-named  substances 
may  be  used  as  condensation  agents  :  hydrochloric  acid,  acetic  anhy- 
dride, as  well  as  primary  and  secondary  amines  (ethyl  amine,  diethyl 
amine,  piperidine,  and  others).  For  the  second  reaction  the  bases 
mentioned  may  be  used.  A  small  quantity  of  one  of  these  may  pro- 
duce large  quantities  of  the  condensation  product  :  this  is  a  case  of  a 
so-called  continuous  reaction.  It  is  probable  that  the  amine  reacts 
first  with  the  aldehyde,  water  being  eliminated  :  i 


N  \NR// 

(R"  =  a  bivalent  radical  or  two  univalent  radicals.) 

In  the  example  above  : 


N(C2H5)2 


/IN  (V^  ons^o 

CH3 . CH IO  +  2H  N(C2H5)2  =  CH3 . CH <  +  H2O 

XN(C2H5)2 


The  aldehyde  derivative  thus  formed  then  acts  upon  the  second  com 
pound  with  the  regeneration  of  the  amine  : 

X  X 

R.CH  =  NR,  +  H2C  =  RNH   +  C=CH.R 


1  B.  31,  738. 


TRANSITION  FROM  ALIPHATIC  TO  AROMATIC  SERIES   2O/ 


H\  CH  =  2  HNR, 


R         X 

I  I 

-  CH  -  CH 
i 
Y 


In  the  above  example : 


CH3                       R 
CO                         CH 

CH3 
CO 

CHH  +  tfCc5yTN(QH,)j 

f  HCH 

COOC2H5 

COO 

CH, 


CH3 

CO      CH3      CO 

=  2  NH(C2H5)2  -f  CH  -  CH  -  CH 

C( 


COOC2H5       COOC2H 

The  amine  thus  regenerated  carries  over  anew  the  aldehyde  residue  to 
the  acetacetic  ester,  and  so  on. 

According  to  Rabe  (A.  323,  83  and  332,  i),  the  substance  melting  at 
79-80°  does  not  possess  the  constitution  of  an  ethylidenebisacetacetic 
ester,  but  it  shows  a  desmotropic  modification,  forming  a  cyclic  com- 
pound as  follows : 


C2H5OOC  -  CH  -  CO 

CH..CH  CH0H 


C2H5OOC  -  CH  -  CO  -  CH3 

Ethylidenebisacetacetic  ester"  (liquid ) 


C2H5OOC  -  CH  -  CO 
CH3.CH  CH2 

C2H5OOC  -  CH  -  C  -  OH 
\CH3 

Dimethylcyclohexanoldicarbonic  ester 
(m.  p.  79-80°) 


But  compare  the  objections  of  Knoevenagel  (B.  36,  2118). 

2.  Of  the  compounds  which  can  be  obtained  by  reaction  (2),  of 
especial  interest  are  those  which,  like  the  ethylidenebisacetacetic  ester 
prepared  above,  contain  two  carbonyl  groups  (i.5-diketones)  and  in 
addition  a  methyl  group.  If  such  compounds  are  treated  with  those 


208 


SPECIAL   PART 


substances  which  have  the  power  to  eliminate  water  (alkalies  or  acids), 
six-membered  carbon  rings  are  formed  as  follows : 


R.CH 
X.CH- 


X . CH  -  CO 


CO    -CH, 


In  the  above  example : 

JO 
CHQ.CH 


CoH.OOC 


>CH- 


X  -  CH  -  CO 

R    ^  \* 

K.  .  \^ri  V^rl 

X  -  CH  -  C  -  CH3 
C9H,OOC  -  CH  -  CO 


H       =  H9O  + 
-CH3 


CH, 


C2H5OOC 


.CH  CH 

-\H-/-C 


According  to  Rabe,  ring  formation  takes  place  as  indicated  above, 
and  the  change  at  this  stage  is  as  follows : 


C2H5OOC  -  CH  -  CO 

CH3 .  CH  CH 

=  H20  +  S 

C2H,OOC  -  CH  -  C  -  CH3 


C2H5OOC  -  CH  -  CO 

CH3.CH       •       CHjH"' 

C2H5OOC  -  CH  -  C  —    !  OH 
\CH3— 

Beside  this  ring  closing,  a  second  reaction  takes  place  in  the  experiment 
made  above.  The  sulphuric  acid  saponifies  the  primarily  formed  acid- 
ester,  with  the  elimination  of  carbonic  acid : 


H 

OOC.CH-CO 
\ 


\          S 

:.CH-C- 


CH  =  2  C02  +  2  C2H5OH  +  CH 


CH, 


CH2-CO 

,-CH  CH 

\  // 

CH2-C-CH3 

Dimethylcyclohexenone 


This  ring  closing  with  1.5  diketones  is  capable  of  many  modifications. 
By  using  formaldehyde,  acetaldehyde,  proprionaldehyde,  benzaldehyde, 
etc.,  R  =  H,  CH3,  C2H5,  C6H5,  etc.  By  using  acetaceticester,  acetylace- 
tone,  benzoylacetone,  etc.,  X  =  COOC,H.,  CH3CO,  CCH5CO,  etc. 

The  many-sidedness  of  the  reaction  is  materially  increased  by  starting 
with  the  unsymmetrical  1.5  diketone,  e.g.: 


TRANSITION  FROM  ALIPHATIC  TO  AROMATIC  SERIES    2OQ 


f"     I 

CO      R         CO 
CH  -  CH  -  CH 
:OOC2H5     COOC2H5 

The  nature  of  the  reaction  requires,  however,  that  one  of  the  two  car- 
bonyl  groups  must  be  connected  with  a  methyl  group,  otherwise  the 
elimination  of  water  cannot  take  place.  The  compounds  so  obtained 
are  all  derivatives  of  the  mother  substance  : 

CH2  -  CO 
CH 


which  is  called  cyclohexenone,  and  which  may  be  considered  as  the 
keto-derivative  of  tetrahydrobenzene 


CH2-CH2 

<fH2  CH 

CHo  -  CH 


This,  therefore,  is  a  transition  from  the  aliphatic  to  the  (hydro)  aromatic 
series. 

This  primarily  obtained  compound  may  by  different  reactions  be 
converted  into  other  hydroaromatic  and  aromatic  substances.  If,  e>g-, 
the  dimethylcyclohexenone  be  reduced,  the  ketone  group  is  converted 
into  the  secondary  alcohol  group,  at  the  same  time  the  double  union  is 
severed,  and  two  hydrogen  atoms  are  added  on,  so  that  there  is  obtained 
an  alcohol  derivative  of  hexahydro-benzene  or  -xylene. 

OH 

CH2  -  CH 
CH3  -  CH  CH2 

CH2  -  CH  -  CH3. 

Hexahydroxylenol 

If  this  compound  be  oxidised,  the  secondary  alcohol  group  is  changed 
to  a  ketone  group,  and  a  keto-derivative  of  a  hexahydroxylene  is  formed : 


210  SPECIAL  PART 

CH2  -  CO 
CH3  -  CH  CH2 

CH2  -  CH  -  CH3 

If  the  hexahydrogen  addition  alcohols  be  treated  with  substances  hav- 
ing the  power  to  eliminate  water,  there  is  obtained  a  tetrahydrogen 
addition  product  of  the  hydrocarbon,  e.g.  : 

CH2  -  CH 

/  % 

CH3  .  CH  CH  =  Tetrahydroxylene 

CH2-CH.CH3 

If  in  compounds  like  hexahydroxylenol,  the  hydroxyl  be  replaced  by 
iodine,  and  the  resulting  iodide  reduced,  there  is  obtained  a  hexahy- 
drogen addition  product  of  the  hydrocarbon,  e.g.  : 

CH2  -  CH2 

CH3  .  CH  CH2  =  Hexahydroxylene 

CH2-CH.CH5 

It  is  thus  evident  that  the  syntheses  of  a  great  variety  of  hydroaromatic 
compounds  are  possible. 

3.  By  these  reactions  the  compounds  of  the  pure  aromatic  series 
may  be  reached.  If  bromine  be  allowed  to  act  on  the  primarily  arising 
ring  compound,  as  has  been  done  practically,  the  double  union  is  broken 
up  by  the  addition  of  two  atoms  of  bromine  : 

CO 
CHBr 


CH2 

-CO 

CH2 

CH3.CH 

a 

H  +  Br2  =  CH3.CH 

\ 

A 

V 

CH2 

-C  - 

CH,                      CH2 

/ 
-  CBr  - 


CH 


These  dibromides  are  very  unstable,  and  even  in  the  cold  give  off  two 
molecules  of  hydrobromic  acid  : 

CH,  -  CO  CH2  -  CO 


CH  -C-CH, 


TRANSITION  FROM  ALIPHATIC  TO  AROMATIC  SERIES    211 

Finally,  this  unstable  keto-form  (CH2-CO)  changes  itself  into  the 
stable  enol-form  (CH  =  C  .OH),  and  the  s-xylenol  is  obtained. 


OH 

CH  =  C 
CH.C 

CH-C 


CH 


For  further  information  concerning  the  transition  from  aliphatic 
to  aromatic  or  hydroaromatic  compounds,  compare  Bernthsen,  XI  Ed., 
p.  382;  Richter,  X  Ed.,  Vol.  II,  pp.  4-6,  and  35;  Krafft,  IV  Ed., 
p.  446;  Meyer- Jacobson,  II  Vol.,  p.  79. 


212  SPECIAL  PART 

II.   AROMATIC   SERIES 

1.  REACTION:  NITRATION  OF  A  HYDROCARBON 

EXAMPLES:  Nitrobenzene  and  Dinitrobenzene l 

Nitrobenzene 

To  150  grammes  of  concentrated  sulphuric  acid  contained  in  a 
J-litre  flask,  add  gradually,  and  with  frequent  shaking,  100  grammes 
of  concentrated  nitric  acid  (sp.  gr.  1.4).  After  cooling  the  mix- 
ture to  the  room  temperature,  by  immersion  in  water,  gradually 
add  50  grammes  of  benzene,  with  frequent  shaking.  If  the  tem- 
perature should  rise  above  50-60°,  the  operation  is  interrupted, 
and  the  flask  immersed  in  water  for  a  short  time.  When  all  of  the 
benzene  has  been  added,  a  vertical  air  condenser  is  attached  to 
the  flask ;  it  is  then  heated  in  a  water-bath  for  an  hour  at  60* 
(thermometer  in  the  water)  ;  during  the  heating  the  flask  is  fre- 
quently shaken.  After  cooling,  the  lower  layer,  consisting  of  sul- 
phuric and  nitric  acids,  is  separated  from  the  upper  layer  of 
nitrobenzene  in  a  separating  funnel.  The  nitrobenzene  is  then 
agitated  in  the  funnel  several  times  with  water  :  it  must  be  borne 
in  mind  that  the  nitrobenzene  now  forms  the  lower  layer.  After 
being  washed,  it  is  placed  in  a  dry  flask,  and  warmed  on  a  water- 
bath  with  calcium  chloride  until  the  liquid,  milky  at  first,  becomes 
clear.2  It  is  finally  purified  by  distillation  from  a  fractionating 
flask  provided  with  a  long  air  condenser.  Boiling-point,  206-207°. 
Yield,  60-70  grammes. 

Dinitrobenzene 

To  a  mixture  of  25  grammes  of  concentrated  sulphuric  acid  and 
15  grammes  of  fuming  nitric  acid,  10  grammes  of  nitrobenzene  are 

1  A.  9,  47 ;  12,  305.    Ostwald's  Klassiker  der  exacten  Wissenschaften  Nr.  98. 

2  The  crude  product,  separated  from  the  acid  and  treated  with  water,  may  also  be 
distilled  with  steam.     The  higher  nitro  derivatives  are  not  volatile  with  steam. 
The  distillate  is  now  treated  as  above. 


AROMATIC   SERIES  213 

gradually  added  (hood)  ;  the  reaction-mixture  is  then  heated  for 
half  an  hour  on  a  water- bath,  with  frequent  shaking;  after  cooling 
somewhat,  it  is  poured,  with  stirring,  into  cold  water.  The  dinitro- 
benzene  which  solidifies  is  filtered  off,  washed  with  water,  pressed 
out  on  a  porous  plate,  and  recrystallised  from  alcohol.  Melting- 
point,  90°.  Yield,  10-12  grammes. 

The  property  of  yielding  nitro-derivatives,  when  treated  with  nitric 
acid,  is  a  characteristic  of  aromatic  compounds.  According  to  the 
conditions  under  which  the  nitration  is  carried  out,  one  or  more  nitro- 
groups  can  be  introduced  at  the  same  time.  The  above  reactions  take 
place  in  accordance  with  the  following  equations : 

C6H6  +  N02 .  OH  =  C6H5 .  NO2  +  H2O, 

C6H5 .  NO2  +  NO2 .  OH  =  C6H4 .  (NO2)2  +  H2O. 

If  a  saturated  aliphatic  residue  is  present  in  an  aromatic  compound, 
the  nitration  under  the  above  conditions  always  affects  the  benzene 
ring,  and  not  the  side-chain.  Since  the  benzene  carbon  atoms  are  in 
combination  with  only  one  hydrogen  atom,  the  nitro-compounds  ob- 
tained on  nitration  are  tertiary ;  they  therefore  do  not  have  the  power 
to  form  salts,  nitrolic  acids,  or  pseudo-nitroles,  like  the  primary  and 
secondary  nitro-compounds. 

Recently  the  nitro-group  has  been  introduced  directly  into  the  side- 
chain.1  If,  e.g.,  toluene  or  ethyl  benzene  be  heated  with  weak  nitric 
acid  (sp.  gr.  1.076)  in  a  bomb  up  to  about  100°,  phenylnitromethane, 
C6HS .  CH2 .  NO2 ,  or  phenylnitroethane,  C6H5 .  CH  .  NO2 .  CH3  is  ob- 
tained. 

Not  only  can  the  mother  substances,  the  aromatic  hydrocarbons,  but 
all  their  derivatives,  as  phenols,  amines,  aldehydes,  acids,  etc.,  undergo 
similar  reactions.  But  the  nitration  does  not  take  place  in  every  case 
with  the  same.  ease.  In  each  case,  therefore,  the  most  favourable  con- 
ditions for  the  experiment  must  be  determined.  If  a  compound  is  very 
easily  nitrated,  the  nitration  may  be  effected,  according  to  the  condi- 
tions, by  nitric  acid  diluted  with  water,  or  the  substance  may  be  dis- 
solved in  a  solvent  which  is  not  attacked  by  nitric  acid ;  glacial  acetic 
acid  is  frequently  used  for  this  purpose,  and  then  treated  with  nitric 
acid.  The  reverse  process  may  also  be  employed,  i.e.  the  substance  is 
added  to  a  mixture  of  nitric  acid  and  water,  or  nitric  acid  and  glacial 
acetic  acid.  If  a  substance  is  moderately  difficult  to  nitrate,  it  is  added 

1  B.  27.     Ref.  194  and  468. 


214  SPECIAL   PART 

to  concentrated  or  fuming  nitric  acid.  If  the  nitration  is  difficult,  the 
elimination  of  water  is  facilitated  by  the  addition  of  concentrated  sul- 
phuric acid  to  ordinary  or  fuming  nitric  acid.  In  the  nitration,  tha 
substance  may  either  be  added  to  the  mixture  of  nitric  acid  and  sulphuric 
acid,  or  the  nitric  acid  is  added  to  the  substance  dissolved  in  concen- 
trated sulphuric  acid.  In  working  with  sulphuric  acid  solutions,  at  times 
either  potassium  nitrate  or  sodium  nitrate  may  be  used  instead  of  nitric 
acid.  The  three  nitration  methods  just  described  may  be  still  further 
modified  in  two  ways:  (i)  the  temperature  may  be  varied;  (2)  the 
quantity  of  nitric  acid  may  be  varied.  The  nitration  can  be  effected  in 
a  freezing  mixture,  in  ice,  or  in  water,  by  gentle  heating,  or  finally,  at 
the  boiling  temperature.  Further,  the  theoretical  amount  of  nitric  acid, 
or  an  excess,  may  be  used.  In  order  to  determine  which  of  these  nu- 
merous modifications  will  give  the  best  results,  preliminary  experiments 
on  a  small  scale  must  be  made.  Since  the  nitro-compounds  are  gener- 
ally insoluble  in  water,  or  difficultly  soluble,  they  can  be  separated  from 
the  nitrating  mixture  by  diluting  it  with  water,  or  in  many  cases  better, 
with  a  solution  of  common  salt. 

The  chemical  character  of  a  substance  is  not  changed  in  kind,  but  in 
degree,  by  the  introduction  of  a  nitro-group.  Thus,  the  nitro-derivatives 
of  the  hydrocarbons  are  indifferent  compounds  like  the  hydrocarbons. 
If  a  nitro-group  is  introduced  into  a  compound  of  an  acid  nature  like 
phenol,  it  becomes  more  strongly  acid,  e.g.  the  nitro-phenols  are  more 
strongly  acid  than  phenol.  When  a  nitro-group  is  introduced  in  a  basic 
compound,  the  resulting  substance  is  less  basic ;  e.g.  nitro-aniline  is  less 
basic  than  aniline. 

The  great  importance  of  the  nitro-compounds  is  due  to  their  behav- 
iour on  reduction ;  this  will  be  considered  under  the  next  preparations. 

Concerning  the  introduction  of  the  nitro-group,1  the  following  laws 
are  of  general  application. 

The  introduction  of  one  nitro-group  in  the  benzene  molecule  can, 
obviously,  only  result  in  the  formation  of  one  mononitrobenzene.  If  an 
alkyl  radical  is  present  in  the  benzene  molecule,  the  riitro-groups  enter 
the  ortho-  and  para-,  but  only  to  a  slight  extent  the  meta-position  to  the 
radical.  On  nitrating  toluene,  e.g.,  there  are  formed  almost  exclusively : 

CH3  CH3 

I  I 


NO2 


and 


NO, 


1  The  same  laws  apply  also  to  the  introduction  of  halogen  and  sulphonic  acid 
groups. 


AROMATIC   SERIES  21  5 

The  nitro-groups  seek  the  same  position  when  a  benzene-hydrogen 
atom  has  been  substituted  by  hydroxyl.  Thus,  e.g.,  phenol  gives  on 
nitration  a  mixture  of  o-  and  p-nitrophenol.  On  the  other  hand,  if  a 
compound  contains  an  aldehyde-,  carboxyl-,  or  cyanogen-group,  on  ni- 
tration the  nitro-group  goes  in  the  meta-position  to  this.  Benzaldehyde, 
benzoic  acid,  and  benzonitrile  give  on  nitration  respectively  : 

CHO  CO.  OH 


If  a  compound  already  contains  a  nitro-group,  a  second  one  will  take 
the  meta-position  to  this.  Thus,  on  nitrating  nitrobenzene,  m-dinitro- 
benzene  is  formed.  O-nitrotoluene  or  o-nitrophenol  yield  on  nitrating  : 


NO2 

respectively. 

From  m-nitrobenzoic  acid  the  following  dinitrobenzoic  acid  is  formed  : 

CO.  OH 
N02. 

The  nitro-compounds  are  in  part  liquids,  in  part  solids ;  in  case 
these  latter  distil  without  decomposition,  they  possess  a  higher  boiling- 
point  than  the  mother  substance. 

2.   REACTION.:    REDUCTION   OP    A  NITRO-COMPOUND    TO   AN   AMINE 

EXAMPLES:  (i)  Aniline  from  Nitrobenzene1 

(2)  Nitroaniline  from  Dinitrobenzene 

A  mixture  of  90  grammes  of  granulated  tin 2  and  50  grammes 
of  nitrobenzene  is  placed  in  a  i^-liter  round  flask.  To  this  are 
gradually  added  200  grammes  of  concentrated  hydrochloric  acid 

1  A.  44,  283. 

2  If  granulated  tin  is  not  at  hand,  it  may  be  prepared  by  melting  block-tin  in  an 
iron  spoon  over  a  blast  flame.     The  molten  mass  is  allowed  to  fall  in  drops  into  a 
pail  of  water  from  a  height  of  5-1  metre. 


2l6  SPECIAL   PART 

in  the  following  manner  :  At  first  only  about  one-tenth  of  the 
acid  is  added ;  an  air  condenser,  not  too  narrow,  is  then  attached 
to  the  flask  and  the  mixture  well  shaken.  After  a  short  time  it 
becomes  warm,  and  finally  an  active  ebullition  takes  place.  As 
soon  as  this  happens,  the  flask  is  immersed  in  cold  water  until  the 
reaction  has  moderated.  The  second  tenth  of  the  acid  is  then 
added,  and  the  above  operation  repeated.  After  one  half  of  the 
acid  has  been  used,  the  reaction  becomes  less  violent,  and  the 
second  half  may  be  added  in  larger  portions.  In  order  to  effect 
the  reduction  of  the  nitrobenzene  completely,  the  mixture  is 
finally  heated  one  hour  on  the  water-bath.  To  separate  the  free 
aniline,  the  warm  solution  is  treated  with  100  c.c.  of  water,  then  a 
solution  of  150  grammes  of  caustic  soda  in  200  grammes  of  water 
is  gradually  added.  The  mixture  should  finally  give  a  strongly 
alkaline  reaction.  If  the  action  of  the  caustic  soda  causes  the 
liquid  to  boil,  the  flask  is  cooled  by  water  for  a  short  time,  before 
a  further  addition  of  caustic  soda.  When  all  of  the  solution  has 
been  added,  a  long  condenser  is  attached  to  the  flask,  and  steam 
is  passed  into  the  hot  liquid,  upon  which  aniline,  as  a  colourless 
oil,  and  water  pass  over,  the  aniline  collecting  under  the  water. 
As  soon  as  the  distillate  no  longer  appears  milky,  and  becomes 
clear,  the  receiver  is  changed  and  about  300  c.c.  more  of  the 
liquid  distilled  over.  The  distillates  are  mixed,  treated  with  25 
grammes  of  finely  powdered  sodium  chloride  for  every  100  c.c. 
of  the  liquid,  shaken  until  all  the  salt  is  dissolved,  and  the  aniline 
extracted  with  ether.  After  the  ethereal  solution  has  been  dried 
by  treating  it  with  a  few  pieces  of  solid  potassium  hydroxide, 
the  ether  is  evaporated  and  the  aniline  subjected  to  distillation. 
Boiling-point,  182°.  Yield,  90-100%  of  the  theory.  If  the 
circumstances  are  such  as  not  to  permit  the  experiment  to  be 
completed  without  interruption,  it  is  so  arranged  that  the  neu- 
tralisation with  sodium  hydroxide,  and  the  distillation  with  steam 
immediately  following,  may  take  place  within  a  short  time,  so  that 
the  heat  of  neutralisation  may  be  utilised. 

To  the  nitro-compounds  of  the  aromatic  series,  as  well  as  those  of 
the  aliphatic  series,  belongs  the  property  of  being  converted  into  primary 
amines  on  energetic  reduction.  For  the  reduction  of  every  nitro-group, 


AROMATIC  SERIES  21 7 

six  atoms  of  hydrogen  are  necessary,  and  the  following  equation  is  th« 
general  expression  of  the  reaction  : 

X  .  NO2  +  3  H2  =  X  .  NH2  +  2  H2O. 

For  the  reduction  of  nitro-compounds  on  the  small  scale  in  the 
laboratory,  it  is  most  convenient  to  use,  as  the  reducing  agent,  granu- 
lated tin  and  hydrochloric  acid,  or  stannous  chloride  and  hydrochloric 
acid : 

(1)  2C6H5.NO2  +  3Sn  +  I2HC1  =  2C6H5.  NH2  +  3  SnCl4  +  4H2O, 

(2)  C6H5 .  N02  +  3  SnCl2  +  6  HC1  =  C6H5 .  NH2  +  3  SnCl4  +  2  H2O. 

To  i  molecule  of  a  mononitro-compound,  \\  atoms  of  tin,  or  3  mole- 
cules of  stannous  chloride,  are  therefore  used.  In  calculating  the  amount 
of  the  latter  necessary  for  a  reaction,  it  is  to  be  remembered  that  the  salt 
crystallises  with  two  molecules  of  water  (SnCl2  +  2  H2O).  If  the  re- 
duction is  to  be  effected  by  metallic  tin,  double  the  above  quantity  is 
frequently  used,  i.e.  to  i  nitro-group,  3  atoms  of  tin.  In  this  case,  the 
tin  is  not  converted  into  stannic  chloride,  but  into  stannous  chloride : 

C6H5 .  NO2  +  3  Sn  +  6  HC1  =  C6H5 .  NH2  +  3  SnCl2  +  2  H,O 

Since,  in  the  cases  mentioned,  hydrochloric  acid  is  always  present 
in  excess,  and  the  amines  unite  with  it  to  form  soluble  salts,  the  end 
of  the  operation  occurs  when  no  more  of  the  insoluble  nitro-compound 
is  present,  and  the  reaction-mixture  dissolves  clear  in  water.  In  order 
to  get  the  free  amine  from  the  acid  mixture,  various  methods  may  be 
employed.  If,  as  in  the  above  example,  the  amine  is  volatile  with 
steam,  and  insoluble  in  alkali,  then  the  acid  solution  is  treated  with 
caustic  potash,  or  caustic  soda,  until  the  oxide  of  tin  which  separates 
out  at  first  is  redissolved  in  the  excess  of  alkali ;  the  liberated  amine 
is  driven  over  with  steam.  Further,  volatile  or  non-volatile  amines 
can  be  extracted  from  an  alkaline  solution  by  a  proper  solvent,  like 
ether.  But  this  process  is  often  troublesome,  since  the  alkaline  tin 
solution  forms  an  emulsion  with  ether,  which  subsides  with  great  diffi- 
culty. If  the  free  amine  is  solid,  it  may  be  obtained  by  filtering  off  the 
alkaline  liquid.  In  many  cases,  where  a  non-volatile  amine  is  under 
examination,  it  is  advisable  to  precipitate  the  tin  before  liberating  the 
amine.  This  is  done  by  diluting  the  acid  solution  with  much  water, 
heating  on  the  water-bath,  and  as  soon  as  the  liquid  has  reached  the 
temperature  of  the  bath,  hydrogen  sulphide  is  passed  into  it.  The  tin 
is  precipitated  as  stannous  or  stannic  sulphide ;  this  is  separated  from 


2l8  SPECIAL  PART 

the  amine  hydrochloride  by  filtering.  Since  tin,  in  the  presence  of  a 
large  excess  of  hydrochloric  acid,  is  precipitated  only  with  difficulty  by 
hydrogen  sulphide,  it  is  frequently  necessary  to  drive  off  the  excess 
of  the  acid  before  treating  with  hydrogen  sulphide.  This  is  done  by 
evaporating  to  dryness  on  the  water-bath. 

After  the  tin  sulphide  has  been  filtered  off,  a  portion  of  the  filtrate 
is  tested  with  hydrogen  -sulphide  for  tin ;  if  it  should  be  present,  the 
whole  filtrate  is  evaporated  on  the  water-bath,  as  completely  as  possible, 
to  remove  the  hydrochloric  acid,  then  diluted  with  water,  and  hydrogen 
sulphide  is  again  passed  into  it.  At  times,  the  amine  forms  with 
hydrochloric  acid,  a  difficultly  soluble  salt,  or  the  amine  hydrochloride 
combines  with  the  tin  chloride  to  form  a  difficultly  soluble  double  salt. 
In  this  case,  the  isolation  of  the  amine  may  be  facilitated  by  filtering 
it  off,  washing  with  hydrochloric  acid,  and  pressing  out  on  a  porous 
plate,  if  necessary.  If  one  is  dealing  with  amines,  which,  like  amido- 
acids,  possess  an  acid  character,  obviously,  these  cannot  be  separated 
by  the  use  of  an  alkali,  as  in  the  above  example.  In  a  case  of  this 
kind,  the  tin  is  always  removed  first,  the  acid  solution  evaporated  to 
dryness,  and  the  amido-compound  is  now  liberated  by  the  addition 
of  sodium  acetate.  With  amido-phenols,  sodium  hydrogen  carbonate, 
sodium  carbonate,  or  sodium  sulphite  may  be  used  to  decompose  the 
hydrochloric  acid  salt. 

In  the  laboratory,  other  metals,  like  iron,  zinc,  etc.,  in  connection 
with  an  acid,  are  only  rarely  used  in  the  place  of  tin  or  stannous 
chloride,  for  the  reduction  of  nitro-compounds.  On  the  large  scale, 
iron,  owing  to  its  cheapness,  is  used  in  the  preparation  of  bases  like 
aniline,  toluidine,  a-naphthyl  amine,  etc.,  from  the  corresponding  nitro- 
compounds.  By  the  use  of  iron  and  hydrochloric  acid,  the  reduction 
should  theoretically  take  place  in  accordance  with  the  following  equa- 
tion: 

C6H5.  NO2  +  3  Fe  +  6  HC1  =  3  FeCl2  +  2  H2O  +  C6H5 .  NH2 . 

As  a  matter  of  fact,  on  the  large  scale,  much  less  hydrochloric  acid 
(only  ¥L)  is  used  than  that  required  by  the  above  equation.  In  the 
presence  of  ferrous  chloride,  the  nitro-compound  is  reduced  by  the  iron 
without  the  action  of  hydrochloric  acid,  according  to  the  equation : 

C6H5.  NO2  +  2  Fe  +  4  H2O  =  C6H5.  NH2  +  2  Fe(OH)3 

For  the  neutralisation  of  the  hydrochloric  acid,  a  small  quantity  of 
which  is  always  used  on  the  large  scale,  slaked  lime  is  employed  in 
preference  to  the  more  costly  alkalies. 


AROMATIC  SERIES  2IQ 

The  complete  reduction  of  nitro-compounds  containing  several  nitro- 
groups  is  conducted  in  the  same  way  as  for  mononitro-compounds. 
If  it  is  desired  to  reduce  but  one  or  two  of  several  nitro-groups,  it 
cannot  be  done  by  adding  just  the  calculated  amount  of  the  reducing 
agent ;  for  cases  of  this  kind,  special  methods  are  necessary.  For  this 
purpose,  hydrogen  sulphide  in  the  presence  of  ammonia  or  ammonium 
sulphide  is  often  used  for  the  reduction : 

H2S  =  H2  -f  S 

The  compound  to  be  reduced  is  dissolved  in  water  or  alcohol,  accord- 
ing to  circumstances,  treated  with  ammonia,  heated,  and  hydrogen 
sulphide  passed  into  it ;  or  it  is  heated  in  a  water  or  alcohol  solution 
with  a  previously  prepared  water  or  alcohol  solution  of  ammonium 
sulphide.  In  this  way,  e.g.,  dinitrohydrocarbons  may  be  converted 
into  nitro-amines.  A  second  method,  which  may  be  generally  used  for 
the  reduction,  step  by  step,  of  compounds  containing  several  nitro-groups, 
is  this :  An  alcoholic  solution  of  the  theoretical  amount  of  stannous 
chloride  saturated  with  hydrochloric  acid  is  gradually  allowed  to  flow 
into  an  alcoholic  solution  of  the  substance  to  be  reduced,  which  is  well 
cooled,  and  constantly  shaken.  (B.  19,  2161.) 

EXPERIMENT  : l  The  recrystallised  dinitrobenzene  is  dissolved  in 
alcohol  (4  grammes  alcohol  to  i  gramme  dinitrobenzene),  in  a 
flask,  the  solution  is  quickly  cooled  down,  upon  which  a  portion 
of  the  dinitrobenzene  separates  out ;  it  is  then  treated  with  0.8 
gramme  of  concentrated  ammonia  for  i  gramme  dinitrobenzene 
(the  ordinary  dilute  solution  of  ammonia  employed  as  a  reagent 
must  not  be  used).  After  the  flask  and  its  contents  have  been 
tared,  the  mixture  is  saturated  with  hydrogen  sulphide  at  the 
ordinary  temperature ;  the  current  of  hydrogen  sulphide  is  then 
shut  off,  and  the  flask,  provided  with  a  reflux  condenser,  is  heated 
for  about  half  an  hour  on  a  water-bath.  It  is  then  allowed  to  cool 
to  the  ordinary  temperature,  and  hydrogen  sulphide  again  passed 
into  it  to  saturation,  etc.  This  operation  is  repeated  until  there 
is  an  increase  of  0.6  gramme  in  weight  for  every  gramme  of  dini- 
trobenzene used.  If  in  consequence  of  insufficient  cooling  the 
required  increase  in  weight  does  not  take  place,  hydrogen  sulphide 

i  A.  176   44. 


22O  SPECIAL   PART 

is  again  passed  into  the  mixture.  It  is  then  diluted  with  water, 
the  precipitate  filtered  off,  washed  with  water,  and  extracted 
several  times  by  warming  with  dilute  hydrochloric  acid.  From 
the  acid  filtrate,  the  nitro-aniline  is  set  free  by  neutralising  with 
ammonium  hydroxide  ;  it  is  recrystallised  from  water.  Melting- 
point,  114°.  Yield,  70-80%  of  the  theory. 

/NO9  /NO2 

CflH/        >3H2S=C6H4<(         +2H20  +  3S 
\NO2  \NH2 

Special  methods  are  necessary  for  the  reduction  of  nitro-compounds 
containing  groups  capable  of  being  acted  upon  by  hydrogen,  e.g.,  an 
aldehyde-group,  an  unsaturated  side-chain,  etc.  In  cases  of  this  kind, 
ferrous  hydroxide  is  frequently  used  : 

2  Fe(OH)2  +  2  H2O  =  2  Fe(OH)3  +  H 


2 

The  reduction  is  effected  by  adding  to  the  substance  to  be  reduced, 
in  the  presence  of  an  alkali  (potassium-,  sodium-,  or  barium-hydrox- 
ide), a  weighed  quantity  of  ferrous  sulphate.  By  this  reaction,  o-nitro- 
benzaldehyde  is  reduced  to  o-amidobenzaldehyde  ;  o-nitrocinnamic  acid 
to  o-amidocinnamic  acid. 

As  a  perfectly  neutral  reducing  agent,  which  appears  to  be  well 
adapted  for  a  great  variety  of  reduction  reactions,  aluminium  amalgam1 
is  recommended.  It  is  made  by  treating  aluminium  filings  or  shavings, 
which  have  been  slightly  acted  on  by  caustic  soda,  with  a  solution  of 
mercuric  chloride.  It  reacts  with  water  in  accordance  with  this  equation  : 

Al  +  3  HOH  =  A1(OH)3  +  3  H 

Besides  the  reducing  agents  mentioned,  there  is  still  a  large  number 
of  others  which  find  only  an  occasional  application  in  reducing  nitro- 
compounds  to  amines.  They  will  be  referred  to  under  the  different 
preparations. 

The  primary  mon-amines  are  in  part  colourless  liquids,  e.g.,  aniline, 
o-toluidine,  xylidine  ;  or  colourless  solids  like  p-toluidine,  pseudo- 
cuminidine,  the  naphthyl  amines,  etc.  They  can  be  distilled  without 
decomposition,  are  volatile  with  steam,  and  difficultly  soluble  in  water. 
The  di-  and  poly-amines  are  for  the  most  part  solids,  non-volatile  with 
steam,  and  much  more  readily  soluble  in  water  than  the  mon-amines 

1  B.  38,  1323. 


AROMATIC   SERIES  221 

The  amines  possess  a  basic  character,  but  the  basicity  is  weaker  than 
that  of  the  aliphatic  amines,  in  consequence  of  the  negative  nature 
of  the  phenyl  group. 

Salts:  C6H5.NH2.HC1  .     .     .     .     Aniline  hydrochloride 
C6H5.NH2.HNO3    .     .     .     Aniline  nitrate 
(C6H5.NH2)2.H2SO4   .     .     Aniline  sulphate 

Like  ammonia,  the  amines  unite  with  calcium  chloride  to  form  double 
compounds ;  for  this  reason  they  must  not  be  dried  with  this  substance 
(see  page  54). 

The  primary  mon-amines  find  numerous  applications  in  the  labora- 
tory, as  well  as  on  the  large  scale,  in  consequence  of  their  great  activity. 
Frequent  reference  will  be  made  to  the  subject  in  the  following  pages. 

With  the  aniline  prepared  above,  the  following  experiments  are 
made: 

(1)  Add  3  drops  of  aniline  to  10  c.c.  of  water  in  a  test-tube, 
and  shake  the  mixture.    The  aniline  dissolves.    At  moderate  tem- 
peratures, i  part  of  aniline  dissolves  in  about  30  parts  of  water. 

(2)  Dilute  i  c.c.  of  this  aniline  solution  with  10  c.c.  of  water, 
and  add  a  small  quantity  of  a  filtered  water  solution  of  bleach- 
ing powder.     A  violet  colouration  takes  place ;  by  this  reaction 
(Runge's),  the  most  minute  quantity  of  free  aniline  may  be  de- 
tected.   If  in  this  experiment  the  solution  should  not  remain  clear, 
but  a  dirty  violet  precipitate  separate  out,  a  too  concentrated  solu- 
tion has  been  used ;  the  aniline  water  is  diluted  further,  and  the 
experiment  repeated.     If  a  salt  of  aniline  is  to  be  tested,  it  is  dis- 
solved in  water,  treated  with  alkali,  the  free  aniline  extracted  with 
ether,  this  latter  evaporated,  and  the  residue  dissolved  in  water. 
Then  proceed  exactly  as  just  directed. 

This  reaction  may  also  be  used  to  detect  small  quantities  of 
benzene  or  nitrobenzene.  In  a  test-tube  mix  5  drops  of  concen- 
trated sulphuric  acid  with  5  drops  of  concentrated  nitric  acid, 
then  add  i  drop  of  benzene,  shake,  and  warm  gently  by  passing 
the  tube  through  a  flame  several  times.  Then  add  5  c.c.  of 
water,  and  extract  the  nitrobenzene  with  a  little  ether ;  the  ether 
layer  is  removed  with  a  capillary  pipette,  and  the  ether  evapo- 
rated. The  residue  is  treated  with  i  c.c.  of  concentrated  hydro- 


222  SPECIAL   PART 

chloric  acid,  and  to  this  is  added  a  piece  of  zinc  the  size  of  a 
lentil,  to  effect  the  reduction.  When  the  zinc  is  dissolved,  the 
mixture  is  diluted  with  water,  and  made  strongly  alkaline,  until 
the  hydroxide  of  zinc  precipitated  at  first  is  redissolved ;  the  ani- 
line is  then  extracted  with  a  little  ether.  Then  proceed  as  just 
described. 

If  it  is  desired  to  determine  whether  a  given  compound  is 
nitrobenzene,  it  is  at  once  reduced  with  zinc  and  hydrochloric 
acid. 

(3)  In  a  small  porcelain  dish  place  5  drops  of  concentrated 
sulphuric  acid,  and  with  a  glass  rod  add  i  drop  of  aniline.     The 
aniline  sulphate  thus  formed  solidifies  for  the  most  part  on  the 
rod  ;  remove  it  by  rubbing  it  against  the  walls  of  the  dish.     Then 
add  4  drops  of  an  aqueous  solution  of  potassium  dichromate,  and 
mix  the  liquid  by  revolving  the  dish.    After  a  short  time  the  liquid 
assumes  a  beautiful  blue  colour.     If  the  reaction  does  not  take 
place,  add  2  more  drops  of  the  dichromate,  or  heat  a  moment 
over  a  small  flame. 

(4)  Isonitrile  Reaction  :   Heat  a  piece  of  caustic  potash  the 
size  of  a  bean  with  5  c.c.  of  alcohol,  pour  off  the  solution  from  the 
undissolved  residue  into  another  test-tube ;  the  warm  solution  is 
treated  with  i  drop  of  aniline  and  4  drops  of  chloroform.     A  re- 
action takes  place  immediately,  or  on  gentle  warming;   this   is 
recognised  not  only  by  the  separation  of  potassium  chloride,  but 
by  a  most  highly  characteristic,  disagreeable  odour.     The  odour 
becomes  more  pronounced  on  pouring  off  the  liquid  and  adding 
some  cold  water  to  the  tube.     If  the  vapours  of  the  isonitrile  are 
inhaled  through  the  mouth,  a  peculiar  sweet  taste  is  noticed  in 
the  throat. 

The  reaction  must  be  carried  out  under  a  hood  with  a  good 
draught. 

While  the  two  colour  reactions  with  bleaching  powder  and  chromic 
acid  are  used  especially  for  the  recognition  of  aniline,  the  isonitrile 
reaction  will  show  the  presence  of  any  primary  amine  of  the  aliphatic 
or  aromatic  series.  The  reaction  takes  place  in  accordance  with  the 
following  equation : 

QH5 .  NH2  +  CHC13  =  C6H5 .  NC  +  3  HC1 


AROMATIC   SERIES  223 

For  the  elimination  of  hydrochloric  acid,  caustic  potash   is  added 
Since  all  isonitriles  or  carbylamines  possess  a  characteristic  odour,  on 
the  one  hand  the  smallest  quantity  of  a  primary  base  may  be  detected 
by  this  reaction,  and  on  the  other  a  base  may  be  shown  to  be  primary. 
Secondary  and  tertiary  bases  do  not  give  the  reaction. 

In  the  isonitriles  it  is  very  probable  that  the  carbon  atom  combined 
with  the  nitrogen  atom  is  only  bivalent:  C6H5.  N=C::::.  The  iso- 
nitriles are  isomeric  with  the  acid-nitriles,  e.g.,  C6H5.C=N,  benzo- 
nitrile.  While  the  nitriles  on  saponification  give  acids,  the  isonitriles 
decompose  into  a  primary  amine  and  formic  acid : 

C6H5 .  CN  +  2  H2O  =  C6H5 .  CO .  OH  +  NH3 


3.  REACTION :  (a)  REDUCTION  OF  A  NITRO-COMPOUND  TO  A  HYDROX- 
YLAMINE  DERIVATIVE,  (b)  OXIDATION  OF  A  HYDROXYLAMINE 
DERIVATIVE  TO  A  NITROSO-COMPOUND 

EXAMPLES  :  (a)  Phenylhydroxylamine  from  Nitrobenzene 
(b)  Nitrosobenzene  from  Phenylhydroxylamine 

(a)  Phenylhydroxylamine :  In  a  thick- walled  |-litre  battery  jar 
treat  a  solution  of  5  grammes  of  ammonium  chloride  in  160  c.c.  of 
water  with  10  grammes  freshly  distilled  nitrobenzene.  In  the 
course  of  an  hour  add,  with  constant  stirring,  15  grammes  of  zinc 
dust.  The  jar  containing  the  liquid  is  surrounded  with  water  and 
kept  at  a  temperature  of  13°  (thermometer  in  water ;  small  pieces 
of  ice  are  used  if  necessary).  In  order  to  secure  an  intimate  mix- 
ture, the  zinc  dust  is  divided  into  four  equal  portions,  and  each 
portion  is  added  in  the  course  of  a  quarter  of  an  hour.  After  the 
addition  of  the  last  portion  the*  stirring  is  continued  for  10  minutes ; 
it  is  then  filtered,  using  suction  and  a  Buchner  funnel,  from  the 
zinc  oxide ;  the  filtrate  (solution  I)  is  poured  into  a  beaker,  and 
the  zinc  oxide  deposit  on  the  funnel  is  washed  with  200  c.c.  of 
water  at  45° ;  before  the  water  is  poured  on  the  residue,  the  suc- 
tion is  disconnected  from  the  funnel,  and  is  only  attached  later 
to  draw  the  liquid  through  gently,  drop  by  drop.  The  residue  is 
then  pressed  together  and  filtered  with  strong  suction  (solution  II). 


224 


SPECIAL   PART 


The  two  water  solutions  are  separately  saturated  (with  stirring) 
with  finely  pulverised  salt ;  for  solution  I,  about  45  grammes,  and 
for  solution  II,  about  60  grammes  of  salt  will  be  required.  They 
are  cooled  in  ice  for  15  minutes  to  o°.  The  colourless  crystals 
separating  out  are  filtered  off  with  suction,  and,  without  washing, 
are  pressed  out  on  a  porous  plate.  Yield,  almost  quantitative. 

A  small  test-portion  of  the  crude  product  is  recrystallised  from 
benzene.  Melting-point,  81°.  The  remainder,  without  further 
purification,  is  worked  up  into  nitrosobenzene. 

The  success  of  the  reaction  depends  essentially  upon  the  quality 
of  the  zinc  dust  used.  It  is  therefore  necessary  to  make  a  zinc  dust 
determination  (see  page  390),  and  then  use  about  10%  more  than 
is  required  by  the  theory.  Zinc  dust  of  75%  is  referred  to  above. 

Precautions :  In  the  preparation  of  phenylhydroxylamine,  care 
is  taken  to  prevent  it,  and  particularly  a  warm  solution  of  it,  from 
coming  in  contact  with  the  skin,  since  it  causes  very  painful  and 
annoying  inflammation.  Even  in  pressing  it  out  or  pulverising  it 
under  the  hood,  care  must  be  taken  not  to  breathe  in  any  of  the 
dust,  since  it  causes  extraordinarily  violent  attacks  of  sneezing. 

(fr)  Nitrosobenzene:  To  a  solution  of  30  grammes  of  con- 
centrated sulphuric  acid  in  270  c.c.  of  water,  well  cooled  by  ice 
water,  add  4  grammes  of  freshly  prepared  and  finely  pulverised 
phenylhydroxylamine ;  the  solution  is  then  quickly  treated  with 
an  ice-cold  solution  of  4.6  grammes  of  potassium  dichromate 
in  200  c.c.  of  water ;  the  pure  nitrosobenzene  separates  out  imme- 
diately in  crystals. 

"  On  account  of  the  splendid  phenomena,  steam  should  be 
passed  into  the  liquid  containing  the  oxidation  product ;  the  total 
quantity  of  nitrosobenzene  is  carried  over  in  4—5  minutes.  At  the 
beginning  of  the  heating  the  walls  and  neck  of  the  flask  take  on  a 
deep  green  colour,  and  soon  the  nitrosobenzene  sublimes  in  white, 
lustrous  plates  in  the  bent  tube  entering  the  condenser;  a  few 
moments  later  beautiful  emerald-green  oil  drops  appear  which 
solidify  so  completely,  in  the  lower  part  of  the  condenser,  to  snow- 
white  crystals,  that  the  distillate  presents  the  appearance  of  a 
faintly  green  liquid  containing  only  a  few  minute  crystals.  The 


AROMATIC  SERIES  22$ 

crystals  of  nitrosobenzene  are  pushed  out  of  the  condenser  with  a 
glass  rod,  the  end  being  covered  with  a  cotton  plug,  spread  out 
on  a  porous  plate  and  washed  upon  the  plate  with  ligroin  (boiling- 
point  40-70°).  Melting-point  67.5-68°." 

(a)  The  primary  amines  discussed  in  the  preceding  reaction  are  the 
lowest  reduction  products  of  nitro-compounds.  Recently  two  classes  of 
compounds  have  been  discovered  which  appear  to  be  intermediate  prod- 
ucts between  the  nitro-compounds  and  amines.  In  order  to  distinguish 
them  from  the  compounds  referred  to  in  the  next  preparation,  they  may 
be  called  "  monomolecular  intermediate  reduction  products." 

/H 

C6H5  .  N02  —  *-  C6H,  .  NO  —  »-  C6H5N<        -+  C6H5  .  NH2 

X)H 

Nitrobenzene  Nitrosobenzene     Phenylhydroxylamine  Aniline 

Phenylhydroxylamine1  was  obtained  simultaneously  by  Bamberger 
and  Wohl  by  the  reduction  of  nitrobenzene  with  zinc  dust  in  a  neutral 
solution  : 

/H 

C6H5NO,  +  2  Zn  +  H9O  =  CGH5N<          +  2  ZnO 

XOH 

The  presence  of  certain  salts,  e.g.,  calcium  or  ammonium  chloride,  pro- 
motes the  reaction.  Nitro-compounds  may  also  be  reduced  into 
hydroxylamine  derivatives  by  the  action  of  ammonium  sulphide.2 
Phenylhydroxylamine  acts  like  a  base  towards  acids.  If  it  be  warmed 
with  mineral  acids,  it  undergoes  a  noteworthy  transformation  into 
paraamidophenol  : 

H  NH2 


This  behaviour  explains  the  electrolytic  reduction  of  aromatic  nitro- 
compounds.8 

If  a  nitro-compound  dissolved  in  concentrated  sulphuric  acid  is 
subjected  to  electrolytic  reduction,  not  only  is  the  nitre  -group  reduced 
to  the  amido-group,  but  a  hydroxyl  group  enters  the  para  position  (to  the 
amido-group)  if  it  is  vacant.  Thus  from  nitrobenzene  p-amidophenol 
is  obtained.  In  accordance  with  our  present  knowledge  the  reaction  is 


1  B.  27,  1347,  1432,  1548;  28,  245,  1218.   3  B.  26,  1844,  2810;  27,  1927;  29,  3040 

2  B.  41,  1936. 


226  SPECIAL  PART 

no  longer  considered  remarkable.  Phenylhydroxylamine  is  first  formed, 
which  immediately  undergoes  a  molecular  transformation  into  the 
amidophenol. 

Phenylhydroxylamine  is  a  strong  reducing  agent,  which  reduces 
Fehling's  solution  and  an  ammoniacal  solution  of  silver  nitrate  even  in 
the  cold.  With  nitrous  acid  it  forms  a  nitroso-derivative : 

/H  /NO 

C6H5N<          +  NOOH  =  C6H5N<          +  H2O 

X)H  X)H 

With  aldehydes  it  reacts  thus  : 

/H  /\ 

C6H5 .  N<         +  C6H5 .  CHO  -  C6H5 .  N<      >CH  .  C6H5  +  H2O 

X)H  XK 

By  the  oxygen  of  the  air  it  is  oxidised  to  azoxybenzene  ;  more  energetic 
oxidising  agents  convert  it  into  nitrosobenzene. 

(&}  Nitrosohydrocarbons  may  best  be  obtained  by  the  oxidation  of 
hydroxylamine  derivatives  : 

/H 
C6H5 .  N<        +  O  =  C6H5 .  NO  +  H20 

X)H 

The  nitrosohydrocarbons  in  the  solid  state  form  colourless  crystals, 
but  when  fused  or  in  solution  an  emerald-green  liquid.  They  possess  a 
characteristic  piercing  odour  which  suggests  quinone  and  the  mustard 
oils  ;  they  are  extremely  volatile.  On  reduction  they  go  over  into  amines. 
With  primary  amines  they  combine  to  form  an  azo-compound,  e.g., 

C6H5 .  NO  +  H2N  .  CfiH5  =  C6H5 .  N  =  N .  C6H5  +  H2O 
Combined  with  hydroxylamine  they  form  isodiazo-compounds,  e.g., 


4.   REACTION:   REDUCTION  OF   A  NITRO-COMPOUND  TO  AN  AZOXY-, 
AZO-,  AND  HYDRAZO-COMPOUND 

EXAMPLES  :  Azoxybenzene,  Azobenzene,  Hydrazobenzene 

(i)  Azoxybenzene:1  To  200  grammes  of  methyl  alcohol  con- 
tained in  a  2-litre  flask  provided  with  a  wide  reflux  condenser, 
20  grammes  of  sodium  in  pieces  the  size  of  a  bean  are  gradually 

*  8.15,865. 


AROMATIC   SERIES  22/ 

added ;  the  flask  is  not  cooled  (heat  being  generated  by  the  re- 
action). Since  methyl  alcohol  frequently  contains  much  water, 
the  first  portions  of  the  sodium  must  not  be  added  too  rapidly. 
When  the  metal  is  dissolved,  30  grammes  of  nitrobenzene  are 
added,  and  the  mixture  heated  for  3  hours  on  an  actively  boiling 
water-bath  (reflux  condenser).  Crystals  of  sodium  formate  soon 
begin  to  separate  out ;  this  often  causes  a  troublesome  bumping. 
The  greater  portion  of  the  methyl  alcohol  is  then  distilled  off 
(the  flask  being  placed  in  the  water-bath;  silk  thread).  The 
residue  is  treated  with  water,  and  the  reaction-mixture  poured 
into  a  beaker.  After  long  standing,  especially  in  a  cool  place, 
the  oil  at  the  bottom  solidifies  to  a  bright  yellow  crystalline  mass, 
which  is  separated  from  the  liquid  by  decanting  the  latter ;  it  is 
washed  several  times  with  water  and  finally  pressed  out  on  a 
porous  plate.  If  the  azoxybenzene  does  not  solidify,  the  main 
quantity  of  the  water  solution  is  poured  off  and  the  oil  treated 
with  small  pieces  of  ice.  If  solidification  does  not  take  place 
now,  it  is  due  to  the  presence  of  nitrobenzene ;  this  is  distilled  off 
with  steam,  and  the  difficultly  volatile  residue,  after  it  has  cooled, 
is  further  cooled  with  ice.  From  methyl  alcohol  (use  3  c.c. 
of  the  alcohol  for  every  gramme  of  the  substance)  the  azoxy- 
benzene crystallises  in  bright  yellow  needles,  melting  at  36°. 
Yield,  20-22  grammes. 

(2)  Azobe nze ne ; l  Five  grammes  of  crystallised  azoxybenzene, 
dried  completely  by  heating  on  a  water-bath  for  an  hour,  are  finely 
pulverised  and  intimately  mixed  in  a  mortar  with  15  grammes  of 
coarse  iron  filings,  which  must  also  be  completely  dry ;  the  mixture 
is  distilled  from  a  small  retort,  not  tubulated.  It  is  first  warmed 
with  a  small  luminous  flame  kept  in  constant  motion ;  the  size  of 
the  flame  is  increased  after  some  time ;  finally  the  last  portions 
are  distilled  over  with  a  non-luminous  flame.  If,  on  heating,  a 
sudden  but  harmless  explosion  should  occur,  it  is  due  to  the  fact 
that  the  substances  were  not  dry ;  the  experiment  must  be  re- 
peated. The  reddish  distillate  is  collected  in  a  small  beaker,  and, 
after  it  has  solidified,  is  washed  with  hydrochloric  acid  to  remove 

1  A.  12,  311 ;  207, 329. 


228  SPECIAL    PART 

the  aniline,  then  with  water,  and  pressed  out  on  a  porous  plate, 
The  experiment  is  repeated  a  second  time  with  a  fresh  quantity  of 
azoxybenzene  ;  by  working  carefully  the  same  retort  can  be  used 
again.  The  two  pressed-out  crude  products  are  united.  Azoben- 
zene  crystallises  from  ligroi'n,  after  a  partial  evaporation  of  the 
solvent,  in  the  form  of  coarse  red  crystals  melting  at  68°. 

(3)  Hydrazobenzene  :  l  Dissolve  5  grammes  of  azobenzene  in 
50  grammes  of  alcohol  (about  95%)  in  a  flask  provided  with  a 
reflux  condenser,  and  treat  with  a  solution  of  2  grammes  of  caustic 
soda  in  4  grammes  of  water.  To  the  boiling  solution  gradually 
add  zinc  dust  in  small  portions  (best  by  occasionally  removing 
the  cork)  until  the  orange-coloured  solution  becomes  colourless  : 
about  8  grammes  of  zinc  dust  will  be  necessary.  The  hot  solution 
is  then  filtered  with  suction  (Buchner  funnel)  from  the  excess  of 
zinc;  20  c.c.  of  a  water  solution  of  sulphur  dioxide  and  100  c.c. 
of  water  are  previously  placed  in  the  filter-flask.  The  hydrazo- 
benzene  precipitating  out  of  the  alcoholic  solution  is  quickly 
filtered,  washed  with  water  containing  sulphur  dioxide,  and  pressed 
out  on  a  porous  plate.  .  By  crystallising  from  ligroi'n  it  is  obtained 
pure.  Melting-point,  126°.  Yield,  80-90%  of  the  theory. 

Under  the  influence  of  suitable  reducing  agents,  nitre-compounds 
undergo  a  partial  reduction  in  such  a  way  that  two  molecules  enter  into 
combination.  There  are  thus  obtained  first  the  azoxy-,  then  the  azo-, 
and  finally  the  hydrazo-compound,  which  in  order  to  distinguish  them 
from  the  compounds  obtained  in  Reaction  3  may  be  called  u  dimolecular 
intermediate  reduction  products." 

C6H,.NO          C«H-\  C.H«-NC^.-NH 

- 


2  Mol.  i  Mol.  i  Mol.  i  Mol.  A/r  | 

Nitro-         —  >-         Azoxy-          —  >-       Azo-       -  *~    Hydrazo-     -  >-        A    n?m. 
benzene  benzene  benzene  benzene 

In  order  to  reduce  a  nitro-compound  to  an  azoxy-compound,  either 
sodium  amalgam  or  alcoholic-caustic  potash  or  caustic  soda  is  used. 
With  nitrobenzene,  particularly,  the  reaction  takes  place  most  surely 
by  dissolving  sodium  in  methyl  alcohol  as  above.  The  reducing  action 
of  sodium  methylate  depends  upon  the  fact  that  it  is  oxidised  to 

i  Z.  1868,  437. 


AROMATIC  SERIES  22Q 

sodium  formate,  two  hydrogen  atoms  of  the  methyl  group  being  re« 
placed  by  one  atom  of  oxygen  : 

CH3.ONa  +  O2  =  H2O  +  H.CO.ONa 

In  the  operation  carried  out  above  the  reaction  is  expressed  by  the 
equation  : 


=2C°H<7> 

CJI/.N/ 


+  3  H.CO.ONa  +  3  H2O 


A  few  words  may  be  said  here  concerning  the  relatively  weak  reducing 
power  of  previously  prepared  alcoholates,  in  comparison  with  the 
extremely  energetic  action  of  a  mixture  of  undissolved  sodium  and 
alcohol.  While  the  previously  prepared  alcoholates  can  generally 
only  abstract  oxygen,  the  mixture  just  referred  to  belongs  to  the  class 
of  very  strong  reducing  agents.  With  the  aid  of  this,  it  is  possible  to 
break  up  the  double  or  centric  union  of  the  benzene  ring,  and  thus 
prepare  hydrogen  derivatives  of  benzene.  In  this  case  the  alcoholate 
does  not  act  as  a  reducing  agent  as  above,  but  the  hydrogen  effects  the 
reduction : 

CH3.OH  +  Na  =  CH3.ONa  +  H 

The  azoxy-compounds  are  yellow-  to  orange-red  cry  stall  isable  sub- 
stances, which,  like  the  nitro-compounds,  are  of  an  indifferent  charac- 
ter; but  they  are  not  volatile  with  steam,  and  cannot  be  distilled 
without  undergoing  decomposition.  On  reduction  they  yield  first 
the  azo-compounds,  then  the  hydrazo-compounds,  and  finally  two 
molecules  of  a  primary  amine.  By  heating  with  sulphuric  acid,  azoxy- 
benzene  is  converted  into  its  isomer  oxyazobenzene : 

C6H5 .  N— N .  C6H5  =  C6H5 .  N=N .  C6H4 .  OH 
O 

If  an  azoxy-compound  is  distilled  carefully  over  iron  filings,  its  oxygen 
atom  is  removed,  and  an  azo-compound  is  formed : 

C6H5.N-N.C6H5  H-  Fe  -  C6H5.N=N.C6H5  +  FeO 
O 

Azo-compounds  may  also  be  obtained  directly  from  nitro-compounds, 
since  they  are  reduced  by  sodium  amalgam,  or,  in  an  alkaline  solution,  by 


230  SPECIAL  PART 

zinc  dust  or  stannous  chloride  (sodium  stannous  oxide).     The  lattei 
reducing  agent  acts  in  accordance  with  this  equation  : 

X)Na 
C6H5.N         / 


\  C6H5.N         \ 

NONa  NO 


Na 

Sodium  stannate 

Azo-compounds  may  also  be  obtained  by  the  oxidation  of  hydrazo 
compounds  : 

C6H5  .  NH  .  NH  .  C6H5  +  O  -  C6H5  .  N=N  .  C6H5  +  H2O 

The  azo-hydrocarbons  are  orange-red  to  red  crystalline  substances 
which  can  be  distilled  without  decomposition,  differing  in  this  respect 
from  the  azoxy-compounds. 

EXPERIMENT:  A  few  crystals  of  azobenzene  are  heated  in  a 
test-tube  to  boiling,  over  a  free  flame.  A  red  vapour  is  evolved, 
which  again  condenses  to  crystals  on  cooling. 

The  azo-compounds  thus  differ  in  their  stability  from  the  very  easily 
decomposable  diazo-compounds,  which  also  contain  the  group  N  =  N, 
but  it  is  in  a  different  combination. 

By  the  reduction  of  an  azo-compound,  a  hydrazo-compound  is  first 
formed  and  finally  an  amine. 


The  hydrazo-compounds  are  formed  by  the  reduction  of  azo-com- 
pounds with  ammonium  sulphide  or  zinc  dust  and  an  alkali.  Zinc  dust 
with  caustic  soda  acts  as  follows  : 

CNa 
_ 


They  may  also  be  formed  on  the  direct  reduction  of  nitro-compounds 
in  alcoholic  solution  by  zinc  dust  and  an  alkali  ;  this  method  is  used 
practically  on  the  large  scale. 

The  hydrazo-compounds,  in  contrast  with  the  azoxy-,  and  especially 
with  the  intensely  coloured  azo-compounds,  are  colourless.  They  are 
derived  from  hydrazine,  NH2  —  NH2,  in  which  one  hydrogen  atom  of 
the  two  amido-groups  has  been  replaced  by  a  hydrocarbon  radical.  The 


AROMATIC  SERIES  231 

basic  character  of  hydrazine  is  so  weakened  by  the  presence  of  the 
negative  hydrocarbon  residues,  that  the  hydrazo-compounds  no  longer 
possess  a  basic  character.  On  oxidation  hydrazo-compounds  pass  over 
to  azo-compounds,  a  reaction  which  takes  place  slowly  but  completely, 
under  the  influence  of  the  oxygen  of  the  air.  The  hydrazo-compounds 
decompose,  on  heating,  into  azo-compounds  and  primary  amines. 

2C6H5.NH.NH.C6H3=C6H5.N— N.C6H5  +  2  C6H5.NH2. 

EXPERIMENT  :  A  few  crystals  of  hydrazobenzene  are  heated  in 
a  small  test-tube  to  boiling ;  the  colourless  compound  becomes 
red,  azobenzene  being  formed.  In  order  to  show  the  presence 
of  aniline,  after  cooling,  the  substance  is  shaken  with  water  and 
the  bleaching-powder  test  applied. 

If  the  hydrazo-compounds  are  treated  with  concentrated  acids  like 
hydrochloric  or  sulphuric  acids,  they  are  converted  into  derivatives 
of  diphenyl : l 

C6H3 .  NH .  NH .  C6H5  =  NH2 .  C6H4 .  C6H4 .  NH2 

p-Diamidodiphenyl  =  Benzidine 

The  molecular  transformation  takes  place  essentially  in  para  position 
to  the  imide  (NH)  groups. 

EXPERIMENT  :  Hydrazobenzene  is  covered  with  concentrated 
hydrochloric  acid,  and  allowed  to  stand  for  about  5  minutes. 
It  is  then  treated  with  water,  and  half  the  solution  is  made  alkaline 
with  caustic  soda :  the  free  benzidine  is  extracted  several  times 
with  ether,  the  ether  evaporated,  and  the  substance  crystallised 
from  hot  water.  Leaflets  of  a  silvery  lustre  are  obtained.  Melt- 
ing-point, 122°.  The  other  half  of  the  solution  is  treated  with 
dilute  sulphuric  acid,  upon  which  the  difficultly  soluble  benzidine 
sulphate  separates  out. 

Benzidine  differs  from  hydrazobenzene,  in  that  it  is  a  strong,  di-acid 
primary  base.  It  is  prepared  technically,  since  the  azo  dyes  derived 
from  it  possess  the  important  property  of  colouring  unmordanted  cotton 
fibre  directly ;  for  most  azo  dyes  the  cotton  must  first  be  mordanted. 
The  first  representative  of  these  dyes  made  was  Congo  Red,  prepared 
from  the  bisdiazo-compound  of  benzidine  and  naphthionic  acid.  In  con- 
sequence, the  entire  class  of  these  dyes  is  called  the  "  Congo  Dyes." 

1 J-  pr-  36,  93 :  J-  1863,  424. 


232  SPECIAL   PART 

/NH2 
C6H4.N=N.C10H/ 


In  a  wholly  analogous  manner,  from  o-nitrotoluene  and  o-nitroanisol 
are  prepared  o-tolidine  and  dianisidine,  respectively. 

CH  OCH3 


/NH, 

OCH 

Tolidine  Dianisidine 

If,  in  hydrazo-compounds,  the  para  position  to  the  imido  (NH) 
group  is  occupied  as,  e.g.,  in  p-hydrazotoluene,  then  the  benzidine 
transformation  cannot  occur. 

In  such  cases,  derivatives  of  o-  and  p-amidodiphenyl  amine  are 
formed  through  the  so-called  "Semidine  transformation."1 


NH— NH-/~~\CH 
CH 


CHo.CO.NH- 

N /  \ / 

/ — \  y — \ 

-NH2. 


5.  REACTION :  PREPARATION  OF  A  THIOUREA  AND  A  MUSTARD  OIL 
FROM  CARBON  DISULPHIDE  AND  A  PRIMARY  AMINE 

EXAMPLE  :  Thiocarbanilide  and  Phenyl  Mustard  Oil  from  Carbon 
Bisulphide  and  Aniline 

Thiocarbanilide :    A    mixture    of  40   grammes    of  aniline,   50 
grammes   of   carbon   disulphide,    50    grammes   of   alcohol,    and 

1  B.  26,  681,  688,  699:  A.  287,  97. 


AROMATIC   SERIES  233 

10  grammes  of  finely  pulverised  potassium  hydroxide  is  gently 
boiled   for  3  hours  on  a  water-bath  in  a  flask  provided  with  a 
long  reflux  condenser.      The  excess  of   carbon  disulphide  and 
alcohol  is  then  distilled  off,  the  residue  treated  with  water,  the 
crystals  separating  out  are  filtered  off,  and  washed  first  with  water, 
then  with  dilute  hydrochloric  acid,  and  finally  with  water.     For 
the  preparation  of  phenyl  mustard  oil,  the  crude  product  is  used 
directly,  after  it  has  been  dried  on  the  water-bath.     In  order  to 
obtain  pure  thiocarbanilide,  2  grammes  of  the  dried  crude  product 
are  recrystallised  from  alcohol.     Large,  colourless  tablets  are  thus 
obtained,   which   melt  at    154°.      Yield,   30-35   grammes.      If  a 
mixture  of  equal  parts,  by  weight,  of  aniline,  carbon  disulphide, 
and  alcoho1   (40  grammes  of  each)   placed  in  a  flask  provided 
with  a  reflux  condenser  is  heated,  with  the  addition  of  0.3  gramme 
of  crystallised  sulphur,1  to  gentle  boiling  on  the  water-bath  for 
6  hours,  a  better,  almost  quantitative  yield  of  thiocarbanilide  is 
obtained,  although  a  longer  time  is  required.     After  the  heating, 
proceed  as  above. 

Phenyl  Mustard  Oil :z  In  a  flask  of  about  400  c.c.  capacity 
place  30  grammes  of  the  crude  thiocarbanilide,  and  treat  with 
120  grammes  of  concentrated  hydrochloric  acid;  the  mixture  is 
distilled  by  heating  to  the  boiling-point  of  the  acid,  on  a  sand- 
bath,  with  a  large  flame  under  a  hood.  When  only  about  20  c.c. 
of  the  liquid  remain  in  the  flask,  the  distillation  is  discontinued. 
The  distillate  is  treated  with  an  equal  volume  of  water,  the  mustard 

011  separated  in  a  dropping  funnel,  dried  with  a  little  calcium 
chloride,  and  distilled.     Boiling-point,  222°.     Yield,  almost  quan- 
titative. 

Triphenyl  Guanidine  :  The  residue  remaining  in  the  flask  after 
the  distillation  with  hydrochloric  acid  is  treated  with  100  c.c.  of 
water,  and  then  allowed  to  stand  for  several  hours,  when  colourless 
crystals  of  triphenylguanidine  hydrochloride  separate  out.  These 
are  filtered  off,  and  warmed  with  some  dilute  caustic  soda  solution. 
The  salt  is  decomposed,  and  the  free  base  obtained,  which  on 
recrystallising  from  alcohol  forms  colourless  crystals.  Melting- 
point,  143°. 

l  B.  32,  2245.  «  B.  15,  986.    Z.  1869,  589. 


234  SPECIAL  PART 

Carbon  disulphide  acts  upon  primary  aromatic  amines  (NH2  in  the 
nucleus)  to  form  symmetrical  disubstituted  thioureas,  e.g. 

/NH.C6H5 

CSS  +  2  C6H5 .  NH2  =  C=S  +  H2S. 

\NH.C6H? 

Diphenyl  thiourea  =  Thiocarbanilide 

By  the  addition  of  caustic  potash  the  elimination  of  hydrogen  sul- 
phide is  facilitated,  so  that  the  reaction  takes  place  in  a  shorter  time 
than  without  the  use  of  the  alkali. 

From  the  thioureas  thus  obtained  the  mustard  oils  may  be  prepared 
by  heating  with  acids,  as  hydrochloric  acid,  sulphuric  acid,  phosphoric 
acid.  The  reaction  takes  place  in  accordance  with  the  following 
equation : 


=  C6H5.N=C=S  +  C6 

H5  Phenyl  mustard  oil 

The  primary  amine  formed  in  addition  to  the  mustard  oil  combines 
with  the  acid.  Besides  this  reaction  a  second  one  takes  place,  viz. : 
the  amine  formed  acts  upon  some  still  undecomposed  thiourea,  result- 
ing in  the  formation  of  a  guanidine  derivative : 

/NH.C6H5  /NH.C6H5 

CS  +  C6H6.NH2  =  C=N.C6H5    +  H2S. 

\NH.C6H5  \NH.C6H5 

Triphenyl  guanidine 

/NH2 
Since  guanidine  C~ NH   is  an  extremely  strong  base,  which,  like 


\NH 


caustic  potash  and  caustic  soda,  absorbs  carbon  dioxide  from  the  air, 
the  introduction  of  the  three  negative  phenyl  groups  in  the  above  com- 
pound has  not  neutralised  the  basic  properties  entirely,  and  it  still  has 
the  power  to  form  salts. 

The  aromatic  mustard  oils  are  in  part  colourless  liquids,  in  part  crys- 
tallisable  solids,  the  lower  members  are  easily  volatile  with  steam,  and 
possess  a  characteristic  odour.  In  chemical  behaviour  they  are  very 
active.  If  they  are  warmed  for  a  long  time  with  an  alcohol,  they  com- 
bine with  the  alcohol,  addition  taking  place,  and  a  thiourethane  is 
formed : 

C6H5 .  NCS  +  C2H5 .  OH  =  C6H5 .  NH .  CS .  OC2H5. 

Phenylthiourethanc 


AROMATIC  SERIES  235 

In  the  same  way,  ammonia  and  primary  bases  are  added  with  the 
formation  of  a  thiourea  : 


C6H5.NCS  +  NH3  =  CS 

\NH.C6H5 

Phenylthiourea 

/NH.C6H5 
C6H5  .  NCS  +  C6H5  .  NH2  =  CS 


s-Diphenylthiourea 

EXPERIMENT  :  Treat  2  drops  of  phenyl  mustard  oil  on  a  watch- 
glass  with  2  drops  of  aniline,  and  warm  gently  over  a  small  flame. 
On  stirring  the  reaction-product  after  cooling,  with  a  glass  rod, 
the  thiocarbanilide  will  solidify  in  crystals,  from  which  in  the 
above  reverse  reaction  the  mustard  oil  itself  was  prepared. 

By  heating  with  yellow  mercuric  oxide,  the  sulphur  is  replaced  by 
oxygen,  and  an  isocyanate  is  formed,  which  may  be  easily  recognised 
by  its  extremely  disagreeable  odour  : 

C6H5  .  NCS  +  HgO  =  C6H5  .  NCO  +  HgS. 

Phenyl  isocyanate 

EXPERIMENT  :  Heat  ^  c.c.  of  phenyl  mustard  oil  in  a  test-tube 
with  the  same  volume  of  yellow  mercuric  oxide  for  some  time, 
until  the  oil  boils.  The  yellow  oxide  is  changed  to  the  black 
sulphide,  at  the  same  time  the  extremely  disagreeable  odour  of 
the  phenyl  isocyanate  arises  ;  the  vapour  of  the  compound  attacks 
the  eyes,  causing  tears. 


6.  REACTION:   THE   SULPHONATION  OF  AN  AMINE 
EXAMPLE  :   Sulphanilic  Acid  from  Aniline  and  Sulphuric  Acid1 

To  100  grammes  of  pure  concentrated  sulphuric  acid  in  a  dry 
flask,  30  grammes  of  freshly  distilled  aniline  are  added  gradually, 
with  shaking ;  the  mixture  is  heated  in  an  oil-bath  up  to  1 80- 
190°,  until,  from  a  test-portion  diluted  with  water  and  treated 

1  A.  60,  312;  ioo,  163;  120,  132, 


236  SPECIAL  PART 

with  caustic  soda,  no  aniline  separates  out  :  about  4-5  hours' 
heating  will  be  necessary.  The  cooled  reaction-mixture  is  poured, 
with  stirring,  into  cold  water,  upon  which  the  sulphanilic  acid 
separates  out  in  crystals.  It  is  filtered  off,  washed  with  water,  and 
recrystallised  from  water,  with  the  addition  of  animal  charcoal,  if 
necessary.  Yield,  30-35  grammes. 

When  an  aromatic  compound  is  treated  with  sulphuric  acid,  a  por- 
tion of  the  benzene-hydrogen  is  replaced  by  a  sulphonic  acid  group, 
the  reaction  taking  place  in  accordance  with  the  equation  below.  The 
aliphatic  compounds  do  not  react  in  a  similar  manner.  Under  the 
preparation  of  benzene  sulphonic  acid,  the  details  of  the  reaction  will 

be  discussed. 

X)H       /NH2 

C6H5  .  NH2  +  S02       =  C6H4        +  H20. 


p-Amidobenzenesulphqnic  acid  = 
sulphanilic  acid 

In  the  above  example,  it  happens,  as  in  many  cases,  that  the  sulphonic 
acid  group  enters  in  the  para-position  to  the  amido-(NH2)  group. 
The  amido  sulphonic  acids  are  colourless  crystallisable  compounds 
melting  with  decomposition  ;  they  possess  acid  properties,  i.e.  in  dis- 
solving in  alkalies.  The  basic  character  of  the  amine  is  so  greatly 
weakened  by  the  introduction  of  the  negative  sulphonic  acid  group  that 
the  amido  sulphonic  acids  cannot  form  salts  with  acids.  They  differ 

.  yNH2       N 

in  this  from  the  analogous  carbonic  acids  (  e.g.,  C6H4<  J.  which 

\  \co.onJ 

Amidobenzoic  acid 

dissolve  in  both  acids  and  alkalies. 

The  amido-sulphonic  acids,  since  they  are  derivatives  of  a  primary 
amine,  may  like  them  be  diazotised  by  the  action  of  nitrous  acid  ;  upon 
this  fact  depends  their  great  technical  importance.  If  the  diazo-com- 
pounds  thus  obtained  are  combined  with  amines  or  phenols,  azo  dyes 
are  formed  which  contain  the  sulphonic  acid  group,  and  in  the  form  of 
their  alkali  salts  are  soluble  in  water.  Sulphanilic  acid  particularly, 
and  its  isomer,  metanilic  acid,  obtained  by  the  reduction  of  m-nitro- 
benzenesulphonic  acid,  as  well  as  the  numerous  mono-  and  poly-sul- 
phonic  acids  derived  from  a  and  (3  naphthyl  amines,  find  extensive 
technical  application  in  the  manufacture  of  azo  dyes. 


AROMATIC  SERIES  237 

1.  REACTION:    REPLACEMENT    OF   THE   AMIDO-  AND  DIAZ-GROUPS 
BY  HYDROGEN 

EXAMPLE  :  Benzene  from  Aniline 

Dissolve  5  grammes  of  aniline  in  a  mixture  of  15  grammes  of 
concentrated  hydrochloric  acid  and  30  c.c.  of  water ;  cool  with 
ice,  and  treat  with  a  solution  of  5  grammes  of  sodium  nitrite  in 
15  c.c.  of  water,  until  free  nitrous  acid  may  be  recognised  with 
starch-potassium-iodide  paper.  The  diazobenzenechloride  solu- 
tion thus  obtained  is  allowed  to  flow  carefully  into  a  solution  of 
10  grammes  caustic  soda  in  30  c.c.  of  water  contained  in  a  400  c.c. 
flask  which  is  well  cooled  with  ice.  Further,  dissolve  20  grammes 
of  stannous  chloride  in  50  c.c.  of  water,  and  treat  this  solution 
with  a  concentrated  solution  of  sodium  hydroxide  (2  parts  to  3  of 
water),  until  the  precipitate  at  first  formed  (stannous  oxide)  is 
redissolved  in  the  excess  of  the  alkali.  Treat  the  alkaline  diazo- 
benzene  solution,  well  cooled  with  ice-water,  gradually  with  small 
portions  of  the  sodium-stannous  oxide  solution,  previously  well 
cooled,  waiting  after  each  addition  until  the  lively  evolution  of 
nitrogen  has  ceased  before  adding  more.  When  all  the  reducing 
liquid  has  been  added,  the  flask  is  connected  with  a  condenser, 
and  the  liquid  heated  to  boiling.  The  benzene  formed  passes  over 
first,  and  is  collected  in  a  test-tube.  By  a  careful  distillation  from 
a  small  fractionating  flask  (without  condenser),  it  is  obtained  per- 
fectly pure.  Boiling-point,  81°.  Yield,  3-4  grammes. 

As  already  mentioned,  under  the  preparation  of  methyl  amine,  the 
behaviour  of  the  aliphatic  primary  amines  toward  nitrous  acid  is  very 
different  from  that  of  the  aromatic  compounds.  While  the  former  yield 
alcohols  with  the  elimination  of  nitrogen,  the  latter,  in  a  mineral  acid 
solution,  under  the  influence  of  nitrous  acid,  yield  diazo-compounds, 
discovered  by  Peter  Griess,1  in  the  form  of  their  mineral  acid  salts 
CH3 .  NH2  +  NOOH  =  CH8  .  OH  +  N,  +  H,O 

C6H5 .  NH2  +  NOOH  +  HC1  =  CCH, .  NzzN  .  Cl  +  2  H2O 

Diazobenzene  chloride 

it  has  been  held  that  the  mother  substance  of  the  diazo-compounds, 
—  free  diazobenzene  —  possessed  the  constitution: 

in     in 
C0H5  .  N=N  -  OH 


1  A.  137,  39- 


238  SPECIAL   PART 

In  accordance  with  which  the  diazo  salts  were  expressed  by : 

C6H5 .  NzzN  .  Cl  =  Diazobenzene  chloride, 

C6H5 .  N— N .  NO3  =  Diazobenzene  nitrate, 

C6H5 .  N=N .  O .  SO2 .  OH  =  Diazobenzene  sulphate. 

More  recently  this  view  has  been  abandoned,  and  the  one  proposed 
earlier  by  Blomstrand  taken  up.  It  is,  however,  not  accepted  generally. 
According  to  this  conception  the  above  salts  are  represented  thus : 


65 .  ;  C6H5 .  Nf 

\C1  \N03  \O.S02.OH 

In  accordance  with  this  view  the  diazotising  process  consists  in  re- 
placing the  three  hydrogen  atoms  combined  with  a  nitrogen  atorr 
having  a  valence  of  5,  by  a  trivalent  nitrogen  atom  : 


C6H5.N 


+  N 


OOH 


Cl 

Aniline  hydrochloride 


\C1 


To  emphasise  the  similarity  to  ammonium  compounds,  in  which  the 
valence  of  the  nitrogen  atom  is  probably  5,  the  diazo  salts  are  called 
diazonium  salts.  The  diazo-compounds  can  also  form  double  salts,  e.g.: 

C6H5.N=N.Cl.AuCl3    and     (C6H5.  Ni=N.  Cl)2.  PtCl4 

Diazobromides  have  the  power  of  taking  up  two  atoms  of  bromine  to 
form  perbromides : 

C6H5 .  N=N  .  Br  +  Br2  =  C6H5 .  N2 .  Br8 

Diazobenzene  perbromide 

EXPERIMENT  :  Dissolve  i  c.Co  of  aniline  in  an  excess  of  hydro- 
chloric acid,  diazotise  as  above,  and  add  i  c.c.  of  bromine  dissolved 
in  a  water  solution  of  hydrobromic  acid,  or  in  a  concentrated 
solution  of  potassium  bromide.  A  dark  oil  separates  out,  from 
which  the  solution  is  decanted.  It  is  washed  several  times  with 
water ;  on  cooling,  it  solidifies  to  crystals. 

If  ammonia  is  allowed  to  act  on  the  perbromide,  diazobenzeneimide 
is  obtained : 

/N 
C6H6 .  NBr  .  NBr2  +  NH3  =  C6H5 .  N  1 1  +  3  HBr 


1 


\i 

Diazobenzeneimide 


AROMATIC  SERIES  239 

EXPERIMENT  :  The  perbromide  just  obtained  is  covered  with 
water,  and  concentrated  ammonium  hydroxide  added  to  it.  A 
vigorous  reaction  takes  place  with  the  formation  of  an  oil  possess- 
ing a  strong  odour  (diazobenzeneimide). 

Under  the  influence  of  alkalies  the  diazonium  compounds  yield  salts, 
thus  acting  like  acids. 

C6H5 .  N2 .  Cl  +  2  NaOH  =  C6H5 .  N2 .  ONa  +  NaCl  +  H2O 

These  can  exist  in  two  isomeric  modifications.  The  one  primarily 
obtained  is  characterised  by  the  fact  that  in  alkaline  solution  it  unites 
with  phenols  to  form  azo  dyes ;  while  the  second  modification  obtained 
by  a  longer  action  of  the  alkali,  at  higher  temperature  if  necessary,  does 
not  possess  this  property  at  all,  or  only  in  a  slight  degree.  If  they 
(the  latter)  be  treated  with  acids,  they  are  converted  back  into  the 
diazonium  salts,  and  now  have  the  property  of  combining  with  phenols 
in  alkaline  solutions. 

The  view  of  Hantzsch  is  that  the  salts  in  which  the  diazonium  com- 
pound behaves  as  an  acid,  are  not  derived  from  diazonium  hydroxide,  eg. : 

in 

v  /N 
C6H5.N/ 

\OH 

but  they  are  derived  from  a  compound  having  the  following  constitution : 

in       in 
C6H5 .  N  =  N  -  OH 

Consequently,  for  metallic  salts,  the  first  formula  must  be  modified. 
The  differences  underlying  the  constitution  of  the  two  metallic  salts 
are  due  to  stereoisomerism?  e.g.  • 

C,H5.N  C6H5.N 

NaO  .  N  N  .  ONa 

Syn-diazo  compound  Anti-diazo  compound 

Unites  with  phenols  Does  not  unite  with  phenols 

The  principles  underlying  the  space  arrangement  of  the  three  valences 
of  nitrogen,  as  illustrated  in  these  examples,  will  be  discussed  under 
Benzophenoxim.  Compare  Hantzsch  :  "  Die  Diazoverbindungen  "  (Stutt- 
gart, 1902),  also  Hantzsch  :  «  Stereochemie  "  (2  Ed.),  p-  142.  The  salts 
of  the  diazo-compounds  formed  with  acids  are,  in  most  cases,  colourless, 
crystallisable  substances,  easily  soluble  in  water,  insoluble  in  ether. 


240  SPECIAL   PART 

In  order  to  prepare  them  in  the  solid  condition,  various  methods  may 
be  used.  Thus,  e.g.,  the  very  explosive  diazobenzene-nitrate  may  be 
obtained  in  colourless  needles  by  conducting  gaseous  nitrous  acid  into 
a  well-cooled  pasty  mass  of  aniline  nitrate  and  water,  and  treating  the 
diazo-solution  with  alcohol  and  ether.  In  general,  the  solid  diazo-salts 
may  be  prepared  by  adding  to  an  alcoholic  solution  of  the  amine  that 
acid  the  salt  of  which  is  desired,  and  then  treating  the  well-cooled  mix- 
ture with  amyl  nitrite  : 1 

C6H5 .  NH2  +  N02 .  C,Hn  +  HC1  =  C6H5 .  N=N  .  Cl  +  C5Hn  .  OH  +  H2O 

Amyl  nitrite  Amyl  alcohol 

If  the  solid  diazo-compound  does  not  separate  out  at  once,  ether  is 
added.  On  heating,  the  dry  diazo-salts  decompose  either,  as  in  the 
case  of  diazobenzene  nitrate,  with  explosion,  or  a  sudden  evolution  of 
gas  takes  place  without  detonation.  A  few  diazo-compounds  are  so 
stable  that  they  may  be  recrystallised  from  water. 

In  rare  cases  only,  in  working  with  diazo-compounds,  is  it  necessary 
to  isolate  them  in  a  pure  condition ;  generally,  the  very  easily  prepared 
water  solutions  are  used.  These  compounds  were  formerly  obtained 
by  passing  gaseous  nitrous  acid  into  a  salt  of  the  amine  until  it  was 
diazotised.  But  at  present  this  method  is  employed  only  in  rare  cases  ; 
the  free  nitrous  acid  obtained  from  sodium  nitrite  is  used.  In  order  to 
diazotise  an  amine,  a  solution  of  it  in  a  dilute  acid  —  most  frequently 
hydrochloric  acid  or  sulphuric  acid  —  is  first  prepared.  Theoretically, 
two  molecules  of  a  monobasic  acid  are  required  to  diazotise  one  mole- 
cule of  a  monamine : 

CCH, .  NH^  +  NaNO2  +  2  HC1  =  C6H. .  N2 .  Cl  +  NaCl  +  2  H2O 

but  an  excess  is  always  taken,  —  not  less  than  three  molecules  of  hydro- 
chloric acid  or  two  of  sulphuric  acid  to  one  molecule  of  a  monamine. 
In  many  cases,  the  hydrochloride  or  sulphate  of  the  amine  is  difficultly 
soluble  in  water.  Under  these  conditions,  it  is  not  necessary  to  add 
water  until  the  salt  is  entirely  dissolved,  but  the  solution  of  the  nitrite 
may  be  poured  into  the  pasty  mass  of  crystals ;  when  the  undissolved 
salt  is  diazotised,  it  passes  into  solution.  For  the  diazotisation  of  one 
molecule  of  a  monamine,  one  molecule  of  sodium  nitrite  is  necessary, 
theoretically ;  but  since  the  commercial  salt  is  never  perfectly  pure,  it 
is  advisable  to  weigh  off  from  5-10  %  more  than  the  calculated  amount, 
and  to  determine  by  the  method  given  below  when  a  sufficient  quantity 

i  B.  23,  2994. 


AROMATIC  SERIES  241 

of  this  has  been  added.  The  nitrite  is  dissolved  in  water,  generally 
5-10  parts  of  water  to  I  part  of  salt.  The  nitrite  solution  must  be 
added  gradually  to  the  amine  solution,  and  the  liquid  must  not  be 
allowed  to  become  warm.  In  many  cases,  the  experimenter  is  often 
too  careful,  in  that  he  cools  the  amine  solution  with  a  freezing  mixture, 
and  adds  the  nitrite  solution  drop  by  drop  from  a  separating  funnel. 
Frequently  it  is  sufficient  to  place  the  solution  in  a  water-bath  filled 
with  cold  water,  or  ice  is  thrown  into  the  water,  or  the  amine  solution 
is  cooled  by  ice.  It  is  very  convenient  to  cool  the  solution,  not  from 
without,  but  by  throwing  into  it  from  time  to  time  small  pieces  of  ice. 
The  nitrite  solution  may  be  poured  directly  from  a  flask.  If  the  addi- 
tion causes  evolution  of  gas  bubbles  or  vapours  of  nitrous  acid,  the 
temperature  of  the  solution  must  be  lowered  and  the  nitrite  added  more 
slowly.  In  order  to  be  cognisant  of  the  course  of  the  reaction,  as  well 
as  to  be  able  to  determfne  when  it  is  completed,  starch-potassium-iodide 
paper,  prepared  as  follows,  is  used  : 

A  piece  of  starch  the  size  of  a  pea  is  finely  pulverised,  and  added  to 
200  c.c.  of  boiling  water ;  it  is  boiled  a  short  time,  with  stirring.  After 
cooling,  a  solution  of  a  crystal  of  potassium  iodide  the  size  of  a  lentil, 
in  a  little  water,  is  added  to  it.  With  this  mixture,  saturate  long  strips 
of  filter-paper  3  cm.  wide ;  the  strips  are  dried  by  suspending  them 
from  a  string  in  a  place  free  from  acids.  After  drying,  the  strips  are 
cut  up  and  preserved  in  a  closed  vessel. 

In  order  now  to  diazotise  an  amine,  the  cooled  solution  is  first 
treated  with  a  small  portion  of  the  nitrite  solution ;  it  is  well  stirred, 
and  a  drop  of  it  transferred  with  a  clean  glass  rod  to  the  starch- 
potassium-iodide  paper.  If  the  nitrous  acid  is  already  used  up  in  the 
diazotisation,  no  dark  spots  appear,  and  further  portions  of  the  sodium 
nitrite  may  be  added,  the  test  is  again  repeated,  and  so  on.  But  if  a 
dark  spot  is  formed  at  once,  the  nitrous  acid  is  still  present ;  and  in 
this  case,  before  more  of  the  nitrite  is  added,  one  waits  until  the  reaction 
has  been  completed,  and  so  on.  After  the  addition  of  three-fourths 
of  the  nitrite  solution,  larger  quantities  may  be  added  at  one  time,  but 
toward  the  end  of  the  reaction  small  quantities  must  again  be  employed. 
The  diazotisation  is  ended  when,  after  standing  some  time,  the  mixture 
shows  the  presence  of  nitrous  acid.  Since  the  diazotisation  of  the  last 
portions  of  the  amine  often  requires  some  time,  the  addition  of  the 
nitrite  is  not  discontinued  at  once,  even  if  after  one  minute  the  test 
for  nitrous  acid  is  obtained,  but  the  solution  is  allowed  to  stand 
5-10  minutes,  and  is  then  tested  again.  At  times,  it  happens  that  the 
R 


242  SPECIAL  PART 

weighed-off  quantity  of  sodium  nitrite  is  apparently  not  sufficient  to 
complete  the  diazotisation,  and  that  even  after  the  addition  of  a  fresh 
quantity,  the  test  will  not  show  the  presence  of  nitrous  acid.  This 
phenomenon  has  its  cause  generally  in  the  fact  that  the  acid  (hydro- 
chloric or  sulphuric)  has  been  used  up,  and  consequently  the  nitrite 
cannot  enter  into  the  reaction.  Thus,  in  case  the  weighed-off  amount 
of  sodium  nitrite  is  not  sufficient,  some  acid  is  first  added  to  a  small 
portion  of  the  liquid,  and  this  is  then  tested  to  determine  whether  the 
desired  reaction  has  taken  place.  Further,  often  the  diazo-solution 
becomes  cloudy  toward  the  end  of  the  reaction,  or  a  precipitate  sepa- 
rates out.  This  is  the  diazoamido-compound ;  its  formation  is  also 
caused  by  the  lack  of  free  acid.  On  the  addition  of  acid  and  solution 
of  the  nitrite,  the  precipitate  disappears.  The  replacement  of  the 
diazo-group  by  hydrogen  in  the  above  reaction  takes  place  in  accord- 
ance with  the  following  equation  : 

CCH, .  N2 .  OH  +  H2  =  C6H6  +  N2  +  H2O  * 

In  this  way  it  is  possible  in  many  cases  to  replace  a  primary  amido- 
group  by  hydrogen.  Obviously,  such  a  reaction  is  superfluous,  if,  as 
in  the  above  case,  the  amine  is  obtained  by  the  nitration  of  the  hydro- 
carbon and  the  reduction  of  the  nitro-compound.  But  there  are  cases 
in  which  an  amine  is  not  obtained  in  this  way,  and  where  it  is  of 
importance  to  prepare  the  amido-free  compound  (see  below). 

The  replacement  of  a  diazo-group  by  hydrogen  may  be  effected  by 
other  reducing  agents.  If,  e.g.,  a  diazo-compound  is  boiled  with 
alcohol,  the  latter  is  converted  into  aldehyde,  thus  liberating  two 
hydrogen  atoms,  by  which  the  diazo-compound  is  reduced : 

C6H5.Na.OH  +  CH8.CHa.OH  =  C6H6  +  Na  +  CH3.CHO-f  H2O 

Aldehyde 

The  reaction  is  effected  either  by  conducting  gaseous  nitrous  acid  into 
the  boiling  alcohol  solution  of  the  amine,  or  by  heating  the  amine  with 
alcohol  saturated  with  ethyl  nitrite  ;  or  the  boiling  alcohol  solution  of  the 
amine,  acidified  with  sulphuric  acid,  may  be  treated  with  sodium  nitrite. 

At  this  place,  two  examples  may  be  mentioned  which  illustrate  the 
theoretical  as  well  as  the  practical  value  of  the  reaction :  by  the  oxida- 
tion of  a  mixture  of  aniline  and  p-toluidine,  there  is  formed  a  complex 
dye,  para-fuchsine,  the  constitution  of  which  was  unknown  for  a  long 
time.  This  was  first  explained  by  E.  and  O.  Fischer.  They  heated 
the  diazo-compound  of  the  leuco-base  of  the  dye,  paraleucaniline  with 

i  B.  22, 587. 


AROMATIC  SERIES  243 

alcohol,  which  gave  the  mother  substance  —  the  hydrocarbon  triphenyl 
methane  (A.  194,  270). 

As  an  example  of  the  preparation  value  of  the  reaction,  the  following 
case  is  cited : 

No  method  is  known  by  which  m-nitrotoluene  can  be  prepared  on  a 
large  scale  by  the  nitration  of  tuluene ;  this  results  in  the  formation  of 
the  o-  and  p-compounds  mainly.  In  order  to  obtain  the  m-nitrotoluene, 
the  starting-point  is  p-toluidine.  This  is  nitrated,  upon  which  a  nitro- 
toluidine  of  the  following  constitution  is  obtained : 

CH, 


NH2 

If  the  amido-group  is  replaced  by  hydrogen,  using  the  method  last 
described,  the  desired  m-nitrotoluene  is  obtained. 

By  boiling  a  diazo-compound  with  alcohol  the  reaction  may  take  place 
in  a  different  wav  ;  at  times  the  diazo-group  is  not  replaced  by  hydrogen, 
but  by  the  ethoxy  (-OC0H5)  group,  thus  giving  rise  to  a  phenol  ether. 

,.    X  .  N— N .  SO4H  +  C2H5 .  OH  =  X .  OC2H5  +  N2  +  H2SO4 

In  conclusion,  special  attention  is  called  to  the  fact  that  not  only 
aniline  and  its  homologues  can  be  diazotised,  but  all  the  derivatives  of 
these,  as  the  nitro-amines,  halogen-substituted  amines,  ammo-alde- 
hydes, amino-carbonic  acids,  etc. 

8.   REACTION:   REPLACEMENT  OF   THE   DIAZO-GROUP  BY 
HYDROXYL 

EXAMPLE  :  Phenol  from  Aniline 

Pour  20  grammes  of  concentrated  sulphuric  acid  as  rapidly  as 
possible,  with  stirring,  into  50  grammes  of  water ;  to  the  hot 
solution  add  10  grammes  of  freshly  distilled  aniline,  with  stirring, 
by  allowing  it  to  flow  down  the  side  of  the  beaker,  then  add 
100  c.c.  of  water.  After  the  hot  liquid  has  been  cooled  by  im- 
mersion in  cold  water,  it  is  treated  with  a  solution  of  8.5  grammes 
of  sodium  nitrite  in  40  c.c.  of  water,  until  it  shows  a  blue  spot  on 
starch-potassium-iodide  paper.  The  diazobenzene  sulphate  solu- 


244  SPECIAL   PART 

tion  thus  obtained  is  gently  heated  (40-50°)  for  half  an  hour  on 
the  water-bath,  the  phenol  is  then  distilled  over  with  steam,  and 
the  distillate,  after  being  saturated  with  salt,  is  extracted  several 
times  with  ether.  The  ethereal  solution  is  allowed  to  stand  for 
some  time  over  fused  sodium  sulphate.  The  ether  is  then  evapo- 
.  rated,  and  the  residue  of  phenol  is  subjected  to  distillation  in  a 
small  flask.  Boiling-point,  183°.  Yield,  7-8  grammes. 

The  liquid  remaining  back  in  the  flask  after  the  steam  distilla- 
tion is  filtered  hot.  On  cooling,  a  small  quantity  of  oxydiphenyl 
crystallises  out. 

If  a  diazo-compound  is  heated  with  water,  it  will  pass  over  to  a 
phenol  with  the  evolution  of  nitrogen,  e.g.  : 


For  this  reaction  the  diazosulphate  is  most  advantageously  used.  Under 
certain  circumstances,  the  diazochloride  may  also  be  employed.  But 
the  use  of  the  diazonitrate  is  avoided,  since,  in  this  case,  the  nitric  acid 
liberated,  acting  upon  the  phenol,  readily  forms  nitro-compounds.  In 
many  cases,  it  is  more  convenient  not  to  isolate  the  diazo-compound, 
but  to  add  a  water  solution  of  the  calculated  amount  of  sodium  nitrite 
to  a  boiling  solution  of  the  amine  in  dilute  sulphuric  acid.  The  diazo- 
tisation  of  the  substance  and  the  immediate  decomposition  of  the  diazo- 
compound  take  place  in  one  operation. 

The  same  reactions  are  also  applicable  to  substituted  amines,  like 
amido-  carbonic  acids,  amido-sulphonic  acids,  halogen  substituted 
amines,  etc. 

The  oxydiphenyl  obtained  as  a  by-product  is  formed  in  consequence 
of  the  action  of  some  of  the  undecomposed  diazo-compound  on  phenol  : 

C6H5.  N2.  SO4H  +  H  .  QH4.  OH  =  C6H5.  C6H4.  OH  -f  H2SO4  +  N2 
(Compare  B.  23,  3705.) 

9.  REACTION:  REPLACEMENT  OF  A  DIAZO-GROUP  BY  IODINE 
EXAMPLE  :  Phenyl  Iodide  from  .Aniline 

(Phenyliodidechloride,  lodoso-benzene,  Phenyl  iodite,  and 
Diphenyliodonium  iodidi) 

A  solution  of  10  grammes  of  aniline  1  in  a  mixture  of  50  grammes 
of  concentrated  hydrochloric  acid  and  150  grammes  of  water 

1  Twenty  grammes  of  aniline  should  be  used  if  the  Grignard  reaction  is  to  be 
carried  out  later  on. 


AROMATIC  SERIES  345 

cooled  with  ice-water  is  gradually  treated  with  a  solution  of  8.5 
grammes  of  sodium  nitrite  in  40  c.c.  of  water,  until  a  test  will  give 
a  blue  colour  to  the  starch-potassium-iodide  paper.  The  diazo- 
solution  is  then  treated  in  a  flask,  not  too  small,  with  a  solution  of 
25  grammes  of  potassium  iodide  in  50  c.c.  of  water,  the  mixture  is 
allowed  to  stand  several  hours,  being  cooled  by  water,  finally  it  is 
gently  heated  on  the  water-bath  until  the  evolution  of  nitrogen 
ceases.  The  liquid  is  made  strongly  alkaline  with  caustic  soda  or 
caustic  potash,  and  the  iodobenzene  distilled  over  with  steam ; 
the  steam  delivery  tube  should  reach  almost  to  the  bottom  of  the 
flask.  The  iodobenzene  is  separated  from  the  water  in  a  dropping 
funnel,  dried  with  calcium  chloride  and  redistilled.  Boiling- 
point,  189-190°.  Yield,  about  20  grammes. 

If  a  diazoiodide  is  heated,  the  diazo-group  is  replaced  by  iodine,  the 
reaction  taking  place  smoothly  in  most  cases. 

C6H5.N2.I  =  C6H5.I  +  N2 

The  reaction  is  effected  by  diazotising  the  amine  in  a  hydrochloric  acid 
or  sulphuric  acid  solution,  and  then  treating  it  with  potassium  iodide. 
From  the  diazochloride  or  diazosulphate  there  is  formed  a  diazoiodide, 
the  reaction,  in  many  cases,  taking  place  at  the  ordinary  temperature ; 
in  others,  on  heating,  as  above.  Since  the  reaction  occurs  without 
difficulty,  it  is  used  as  the  method  of  preparation  of  many  iodides. 

The  aromatic  iodides  (iodine  in  the  nucleus)  possess  the  noteworthy 
property  of  combining  with  two  atoms  of  chlorine,  the  iodine  previously 
univalent  becoming  trivalent  : 

i  in 

CtHd.l4-0,  =  C8H5.IClf1 

Phenyliodidechloride 

EXPERIMENT  :  A  portion  of  the  phenyl  iodide  obtained  is  dis- 
solved in  five  times  its  volume  of  chloroform,  the  solution  is  cooled 
by  ice  water,  and  a  current  of  dry  chlorine  is  passed  into  it  from 
a  very  wide  delivery  tube,  until  no  more  is  absorbed.  The  crystals 
separating  out  are  filtered  off,  washed  with  a  fresh  quantity  of 
chloroform,  spread  out  in  a  thin  layer  on  a  pad  of  filter-paper, 
and  allowed  to  dry  in  the  air. 

1  J-  Pr-  33.  JS4-  B.  25,  3494 ;  26,  357 ;  25,  2632.  Concerning  aliphatic  iodide- 
chlorides  see  A.  369,  119. 


246  SPECIAL  PART 

If  caustic  soda  is  allowed  to  act  on  an  iodochloride,  the  two  chlorine 
atoms  are  replaced  by  one  oxygen  atom,  and  an  iodoso-compound  is 
obtained  : 

C6H5  .  IC12  +  H2O  =  C6HS  .  l—O  +  2  HC1 

lodosobenzene 

Besides  this  reaction  another  takes  place,  resulting  in  the  formation  of 
an  iodonium  base.  This  formation  is  probably  due  to  the  fact  that  a 
small  part  of  the  iodosobenzene  is  oxidised  to  phenyl  iodite,  and  this 
condenses  with  iodosobenzene,  iodic  acid  being  eliminated  : 

/on 

C6H5  .  I<f         f  I02.  C6H5  =C6H5  -  I  -  C6H5  +  HI03. 


I< 


Hypoth.  lodoso-  OH 

benzene  hydrate  Diphenyliodonium  hydroxide 

This  base  is  present  in  the  alkaline  solution  filtered  off  from  the  iodoso- 
benzene.  If  the  filtrate  be  treated  with  sulphur  dioxide,  this  reduces 
the  iodic  acid  to  hydriodic  acid,  which,  combining  with  the  iodonium 
base,  forms  an  iodide  insoluble  in  cold  water : 

HIO;i  +  3  S02  =  HI  +  3S03 

CTT  T  (~*    TT 

6n5  ^"6n5  "I 

I —  C6H5  —    —  C6H5  +  H2O 

[OH  +  H|I  J 

i 

EXPERIMENT  :  The  iodochloride  is  carefully  triturated  with  dilute 
caustic  soda  in  a  mortar  (for  i  gramme  of  the  iodochloride,  use  a 
solution  of  0.5  gramme  sodium  hydroxide  in  4  grammes  of  water), 
and  allowed  to  stand  over  night.  The  iodosobenzene  is  then 
filtered  off,  washed  with  water,  and  pressed  out  on  a  porous  plate. 

The  alkaline  filtrate  is  treated  with  a  solution  of  sulphur  dioxide 
until  it  smells  strongly  of  it.  The  precipitate  formed  is  filtered 
off  and  dissolved  in  hot  water.  On  cooling,  colourless  needles  of 
diphenyliodonium  iodide  are  obtained. 

The  iodoso-compounds  have  the  power  of  uniting  with  acids  to  form 

/OH 
salts,  in  which  they  act  like  a  di-acid  base,  e.g.,  CGH-.I<f 

\OH 

EXPERIMENT  :  Several  grammes  of  iodosobenzene  are  dissolved 
with  heat  in  as  small  a  quantity  of  glacial  acetic  acid  as  possible  ,• 


AROMATIC  SERIES  247 

the  solution  is  evaporated  on  the  water-bath  to  dryness,  in  a  watch- 
glass,  or  shallow  dish.  The  solid  residue  is  pulverised  and  re- 
crystallised  from  a  little  benzene.  lodosobenzene  acetate  is  thus 

obtained, 

XX)C.CH3 

C6H5.I< 

\OOC.CH3 

in  the  form  of  colourless  prisms,  melting  at  157°. 

The  iodoso-compounds,  on  treatment  with  hydriodic  acid,  are  reduced 
to  iodides,  with  a  separation  of  iodine. 

C6H5 . 10  +  2  HI  =  C6H5. 1  +  I2  +  H2O 

This  reaction  is  used  for  the  quantitative  determination  of  iodoso- 
oxygen. 

EXPERIMENT  :  Some  potassium  iodide  is  dissolved  in  water, 
acidified  with  dilute  sulphuric  acid,  or  acetic  acid,  and  a  few 
grains  of  iodosobenzene  are  added.  The  iodine  separates  out  as 
a  brown  precipitate. 

If  an  iodoso-compound  is  heated  carefully  to  100°,  it  passes  over  to 
an  iodite  (Jodoverbindung)  : 

2C6H5.IO  =  C6H5.I02+         C6Hs.I 

Phenyl  iodite  Phenyl  iodide 

The  same  compound  may  also  be  obtained  by  treating  an  iodoso- 
compound  with  steam. 

EXPERIMENT  :  lodosobenzene  is  treated  in  a  flask  with  enough 
water  to  form  a  thin  paste.  Into  this  steam  is  conducted  (appa- 
ratus for  distillation  with  steam),  until  no  more  phenyl  iodide 
passes  over  with  the  steam  and  all  the  iodosobenzene  has  been 
dissolved.  If  the  phenyliodite  formed  does  not  dissolve  com- 
pletely, water  is  added  until  solution  takes  place.  The  solution 
is  then  evaporated  on  the  water-bath  until  a  test-portion  cooled 
off  yields  an  abundant  crystallisation  of  phenyl  iodite. 

The  iodites,  like  the  iodoso-compounds,  puff  up  and  suddenly  decom- 
pose on  heating.  (Try  it.)  They  also  abstract  iodine  from  hydriodic 
acid,  and  in  double  the  quantity  as  compared  to  the  similar  action  of 
the  iodoso-compounds. 


248  SPECIAL   PART 

CgH, .  IO2  +  4  HI  =  C6H5I  -f  4 1  +  2  H2O 

They  do  not  form  salts  with  acids. 

The  iodonium  bases l  are  prepared  most  conveniently  by  the  action 
of  silver  oxide  on  a  mixture  of  equal  molecules  of  iodoso  and  iodite 

compounds : 

in 
CGH5 . 10  -f  C6H5 . 10a  +  AgOH  -  C6H5 . 1 .  C6H5  +  AgIO3 

OH 

They  are  soluble  in  water,  show  a  strong  alkaline  reaction  like  the 
sulphonium  and  ammonium  compounds,  and  give  with  halogen  hydracids 
precipitates  of  the  corresponding  salts.  If  the  dried  salts  be  heated, 
they  decompose  into  two  molecules  of  the  hydrocarbon  substitution 

product,  e.g. : 

in 
C6H5.I.CCH5  =  2C6H5I 

I 

i 

EXPERIMENT  :  The  diphenyliodonium  iodide  obtained  as  a  by- 
product in  the  preparation  of  iodosobenzene  is  heated  carefully  in 
a  test-tube  over  a  small  flame.  Suddenly  the  substance  begins  to 
melt  in  one  place;  the  fusion  increases,  without  the  need  of 
further  heating,  and  the  whole  mass  boils  up.  lodobenzene,  easily 
recognised  by  its  odour,  is  obtained. 


10.   REACTION:    REPLACEMENT   OF   A   DIAZO-GROUP    BY   CHLORINE, 
BROMINE,   OR  CYANOGEN 

EXAMPLE  :  p-Tolyl  Nitrile  from  p-Toluidine 

Dissolve  50  grammes  of  copper  sulphate  in  200  grammes  of 
water  in  a  2-litre  flask  by  heating  on  the  water-bath;  then  add 
gradually,  with  continuous  heating,  a  solution  of  55  grammes  of 
potassium  cyanide  in  100  c.c.  of  water.  Since  cyanogen  is  evolved, 
the  reaction  must  be  conducted  under  a  hood,  with  a  good  draught, 
and  the  greatest  care  taken  not  to  breathe  the  vapours. 

While  the  cuprous  cyanide  solution  is  further  gently  heated  up 
to  about  60-70°  on  the  water-h?tb,  the  diazotoluenechloride  solu- 

1  B.  27,  426, 502,  and  1592. 


AROMATIC  SERIES  249 

tion  is  prepared  in  the  following  way :  20  grammes  of  p-toluidine 
are  heated  with  a  mixture  of  50  grammes  of  concentrated  hydro- 
chloric acid  and  150  c.c.  of  water  until  solution  takes  place;  the 
liquid  is  then  quickly  immersed  in  cold  water  and  vigorously 
stirred  with  a  glass  rod,  in  order  that  the  toluidine  hydrochloride 
may  separate  out  in  as  small  crystals  as  possible.  A  solution  of 
1 6  grammes  of  sodium  nitrite  in  80  c.c.  of  water  is  then  added 
to  the  amine  hydrochloride,  cooled  by  ice-water,  until  a  perma- 
nent reaction  of  nitrous  acid  upon  the  starch-potassium-iodide 
paper,  is  obtained.  The  diazotoluene  chloride  thus  formed  is 
poured  from  a  flask  into  the  cuprous  cyanide  solution,  with 
frequent  shaking.  After  the  addition  of  the  diazo-solution,  which 
should  require  about  10  minutes,  the  reaction  mixture  is1  heated 
on  the  water-bath  for  about  a  quarter-hour.  The  tolyl  nitrile  is 
then  distilled  over  with  the  steam.  This  operation  must  also  be 
done  under  a  hood  with  a  good  draught,  since  hydrocyanic  acid 
passes  over.  The  nitrile  distils  as  a  yellow  oil,  which  after  some 
time  solidifies  in  the  receiver.  It  is  separated  by  decanting  the 
water,  pressed  upon  a  porous  plate,  and  purified  by  distillation. 
If  the  oil  will  not  solidify,  the  entire  distillate  may  be  taken  up 
with  ether,  the  ethereal  solution  shaken  with  caustic  soda  solution 
to  remove  the  cresol,  and  then,  after  evaporating  the  ether,  the 
residue  remaining  is  distilled  directly,  or,  in  case  it  is  solid,  it  is 
pressed  out  on  a  porous  plate,  as  above,  and  then  distilled.  Boiling- 
point,  218°.  Yield,  about  15  grammes. 

The  diazo-group  cannot  be  replaced  in  the  same  way  by  iodine  as 
by  chlorine,  bromine,  or  cyanogen.  If  a  water  solution  of  a  diazo- 
chloride,  -bromide,  or  -cyanide  is  heated,  a  phenol  is  formed,  as  is  also 
the  case  on  heating  a  diazo-sulphate  : 

C6H5 .  N2 .  Cl  +  H2O  =  C6H5 .  OH  +  N2  +  HC1 

To  Sandmeyer1  we  are  indebted  for  the  important  discovery  that,  if 
the  heating  be  done  in  the  presence  of  cuprous  chloride,  bromide,  01 
cyanide,  the  reaction  taking  place  is  analogous  to  the  one  by  which 
phenyl  iodide  is  formed : 

1  B.  17,  1633  and  2650;  18,  1492  and  1496. 


2JO  SPECIAL  PART 

C6H,.N,.C1    =C6H5.C1    +N2] 
CH  .Ni.Br   =CH  .Br   +N 
CeH5.  N*.  CN  =  C6H5.  CN  +  N!  J 

The  manner  in  which  the  cuprous  salts  act  is  not  known ;  in  any 
case  they  unite  first  with  a  diazo-compound  to  form  a  double  salt, 
which  plays  a  part  in  the  reaction. 

The  reaction  in  the  above  preparation  of  cuprous  cyanide  takes  place 
in  accordance  with  the  following  equation : 

CuSO4  +  2  KCN  =  CuCN2  +  K2SO4 
2  CuCN2  =  Cu2CN2  +  2  CN 

In  order  to  replace  the  diazo-group  by  chlorine  or  bromine,  the 
above  method  is  followed  exactly.  A  diazo-solution  is  first  prepared, 
and  gradually  added  to  a  heated  solution  of  cuprous  chloride  or  bromide. 
With  easily  volatile  chlorine  or  bromine  compounds,  it  is  desirable  to 
use  a  reflux  condenser,  and  to  allow  the  diazo-solution  to  flow  in  from  a 
dropping  funnel.  In  some  cases  it  is  more  advantageous  not  to  use 
a  previously  prepared  diazo-solution,  but  to  proceed  as  follows :  The 
amine  is  dissolved  in  an  acid  solution  of  a  copper  salt ;  this  is  heated, 
and  to  the  hot  solution,  the  solution  of  nitrite  is  added  from  a  dropping 
funnel.  The  diazotisation  and  replacement  of  the  diazo-group  then 
takes  place  in  one  reaction.  If  the  reaction-product  is  not  volatile  with 
steam,  it  may  be  obtained  from  the  reaction-mixture  by  filtering,  or 
extracting  with  ether. 

The  Sandmeyer  reaction  is  capable  of  general  application.  Since 
the  yield  of  the  product  is  generally  very  good,  for  many  substances  it 
is  used  as  a  method  of  preparation.  It  should  be  finally  pointed  out 
that  by  the  replacement  of  the  diazo-group  by  cyanogen  a  new  carbon 
union  takes  place. 


11.  REACTION:  (a]  REDUCTION  OF  A  DIAZO-COMPOUND  TO  A  HY- 
DRA ZINE.  (b)  REPLACEMENT  OF  THE  HYDRAZINE-RADICAL  BY 
HYDROGEN 

EXAMPLES  :   (a)  Phenyl  Hydrazine  from  Aniline 
(b)   Benzene  from  Phenyl  Hydrazine 

(a)  Add  10  grammes  of  freshly  distilled  aniline  to  100  c.c.  of 
concentrated  hydrochloric  acid  in  a  beaker,  with  stirring ;  aniline 
hydrochloride  partially  separates  out  in  crystals.  To  the  mixture, 


AROMATIC   SERIES  251 

cooled  with  ice,  add  slowly  from  a  dropping  funnel,  a  solution  of 
10  grammes  of  sodium  nitrite  in  50  c.c.  of  water,  until  a  test  with 
starch-potassium-iodide  paper  shows  free  nitrous  acid.  In  this 
case  the  strong  acid  solution  must  not  be  brought  directly  upon 
the  test-paper,  but  a  test-portion  is  diluted  with  water  in  a  watch- 
glass  and  then  the  test  applied.  To  the  diazo-solution  add,  with 
stirring,  a  solution  of  60  grammes  of  stannous  chloride  in  50  c.c. 
of  concentrated  hydrochloric  acid  cooled  with  ice ;  a  thick  paste  of 
crystals  of  phenyl  hydrazine  hydrochloride  separates  out.  After 
standing  several  hours  this  is  filtered  off' with  suction  (Biichner 
funnel  and  filter-cloth),  the  precipitate  is  pressed  firmly  together 
on  the  filter  with  a  pestle ;  it  is  then  transferred  to  a  small  flask 
and  treated  with  an  excess  of  caustic  soda  solution.  Free  phenyl 
hydrazine  separates  out  as  an  oil,  it  is  taken  up  with  ether,  the 
ethereal  solution  dried  with  ignited  potash,  and  the  ether  evap- 
orated. For  the  later  experiments  the  phenyl  hydrazine  thus 
obtained  can  be  used  directly.  If  it  is  desired  to  purify  the  sub- 
stance, the  best  method  is  to  distil  it  in  a  vacuum,  or  it  can  be 
cooled  by  a  freezing-mixture,  and  the  portions  remaining  liquid 
are  poured  off.  Yield,  about  10  grammes. 

Since  the  diazotisation  in  a  strong  hydrochloric  acid  solution 
as  well  as  the  filtration  of  strongly  acid  liquids  is  liable  to  mis- 
carry, it  is  better  to  perform  the  experiment  as  follows :  Dissolve 
10  grammes  of  freshly  distilled  aniline  in  a  mixture  of  30  grammes 
of  concentrated  hydrochloric  acid  and  75  c.c.  of  water  and  diazo- 
tise  it  with  a  solution  of  8  grammes  of  sodium  nitrite  in  30  c.c. 
of  water,  the  beaker  being  cooled  with  ice-water.  The  diazo- 
solution  is  saturated  with  finely  pulverised  salt  (about  30  grammes) 
with  shaking  •  the  solution  is  poured  off  from  any  undissolved  salt, 
and  being  cooled  with  ice  is  treated  with  a  cold  solution  of  60 
grammes  of  stannous  chloride  in  25  grammes  of  concentrated 
hydrochloric  acid.  After  several  hours'  standing,  the  phenyl- 
hydrazine  hydrochloride  separates  out,  this  is  filtered  off  with 
suction,  washed  with  a  little  saturated  salt  solution,  pressed  out 
on  a  porous  plate,  and  treated  as  above. 

(b)    In  a  i -litre  flask  provided  with  a  dropping  funnel  and  con- 


252 


SPECIAL   PART 


denser  (Fig.  68)  150  grammes  of  water  and  50  grammes  of  cop- 
per sulphate  are  heated  to  boiling,  then  from  the  funnel  add 
gradually  a  solution  of  10  grammes  of  free  phenyl  hydrazine  in 
a  mixture  of  8  grammes  of  glacial  acetic  acid  and  75  grammes  of 
water.  The  oxidation  of  the  phenyl  hydrazine  proceeds  with  an 
energetic  evolution  of  nitrogen ;  the  benzene  is  immediately  dis- 
tilled over  with  steam  and  collected  in  a  test-tube.  By  another 
careful  rectification  from  a  small  fractionating  flask  (without  con- 


FlG.  68. 

denser),  pure  benzene,  boiling  at  81°,  is  obtained.     Yield,  about 
5  grammes. 

Monosubstituted  hydrazines  of  the  type  of  phenyl  hydrazine  may 
be  obtained  according  to  the  method  of  V.  Meyer  and  Lecco,1  by 
reducing  the  diazo-compounds  with  stannous  chloride  and  hydrochloric 

acid  : 

C6H5 .  N2 .  Cl  +  2  Ha  =  C6H5 .  NH  .  NH2,  HC1 

Phenyl  hydrazine  hydrochloride 

The  reaction  is  always  conducted  as  above  :  The  amine  is  diazotised 
in  a  strong  hydrochloric  acid  solution,  and  then  a  solution  of  stannous 
chloride  in  strong  hydrochloric  acid  is  added  to  it.  Since  the  hydro- 
chlorides  of  the  hydrazines  are  difficultly  soluble  in  concentrated 
hydrochloric  acid,  these  separate  out  directly  on  the  addition  of  the 

i  B.  16,  2976. 


AROMATIC   SERIES  2$ 3 

stannous  chloride,  and  can  easily  be  obtained  pure  by  filtration,  as 
above. 

The  reduction  of  the  diazo-compounds  to  hydrazines  may  be  ac- 
complished by  the  method  of  Emil  Fischer1  which  led  to  the  dis- 
covery of  this  class  of  compounds,  and  also  by  another  method.  If 
neutral  sodium  sulphite  is  allowed  to  act  on  a  diazo-salt,  the  acid 
radical  of  the  diazo-compound  is  replaced  by  a  residue  of  sulphurous 
acid,  e.g.  : 

CCH5 .  N,.  Cl  +  NaSO, .  Na  =  C6H5 .  N2 .  SO3Na  +  NaCl 

Sodium  diazobenzenesulphonate 

If  this  salt  is  now  reduced  with  sulphurous  acid,  or  with  zinc  dust 
and  acetic  acid,  it  takes  up  two  atoms  of  hydrogen  and  is  converted 
into  a  hydrazine  sulphonate  : 

CGH- .  N2 .  SO,Na  +  H2  =  C6H5 .  NH  .  NH  .  SO3Na 

Sodium  phenyl  hydrazine  sulphonate 

If  this  is  heated  with  hydrochloric  acid,  the  sulphonic  acid  group  is 
split  off,  and  phenyl  hydrazine  hydrochloride  is  formed,  which,  on 
evaporation,  crystallises  out : 

C6H5.NH.NH.SO3Na+HCl  +  HOH  =  C6H5.NH.NH2,HCl  +  NaHSO4. 

According  to  this  method,  which  is  slower,  but  cheaper  than  the 
former,  phenyl  hydrazine  is  prepared  on  the  large  scale. 

The  monosubstituted  hydrazines  possess  a  basic  character ;  in  spite 
of  the  fact  that  they  contain  two  ammonia  residues,  they  combine  with 
only  one  molecule  of  a  monobasic  acid,  e.g. : 

C6H,.NH.NH2,  HC1. 

Phenyl  hydrazine  hydrochloride 

Phenyl  hydrazine  reacts  with  aldehydes  and  ketones,  the  two  hydro- 
gen atoms  of  the  amido-groups  unite  with  the  oxygen  atom  of  the 
CHO-  or  CO-groups,  and  are  eliminated  as  water :  2 

C6H , .  CHO  +  C6H  - .  NH .  NH2         =  CCH , .  CH=N .  NH .  C6H5  +  H2O 

Benzaldehyde  Benzylidenephenyl  hydrazone 

C6H5\ 

C6H5 .  CO .  C6H5  +  C6H5 .  NH .  NH2  -  V=N .  NH .  QH5  +  H2Q 

C6H5' 

Benzophenone 


1  A.  190,  67.  2  B.  I7,  572. 


254  SPECIAL   PART 

This  reaction  can  be  used  for  the  recognition  and  detection  ol 
aldehydes  and  ketones.  In  order  to  prepare  a  hydrazone,  formerly  a 
solution  of  i  part  of  phenyl  hydrazine  hydrochloride  and  i|  parts  of 
crystallised  sodium  acetate  in  10  parts  of  water  was  used  as  a  reagent. 
If  this  is  added  to  an  aldehyde  or  ketone,  there  is  formed,  in  many  cases 
at  the  ordinary  temperature,  but  in  others  only  on  heating,  the  hydra- 
zone.  Since,  at  present,  perfectly  pure  free  phenyl  hydrazine  may  be 
purchased  in  the  market,  a  mixture  of  equal  volumes  of  phenyl  hydra- 
zine and  50  %  acetic  acid,  diluted  with  three  times  its  volume  of  water, 
is  used  as  the  reagent. 

EXPERIMENT  :  To  a  mixture  of  4  drops  of  phenyl  hydrazine  and 
5  c.c.  of  water,  add  3  drops  of  glacial  acetic  acid.  To  this  is 
added  2  drops  of  benzaldehyde  (from  a  glass  rod),  and  the  mix- 
ture shaken.  At  first  there  appears  a  milky  turbidity,  but  very 
soon  a  flocculent  precipitate  of  benzylidenephenyl  hydrazone  sepa- 
rates out.  The  smallest  quantity  of  benzaldehyde  may  be  recog- 
nised in  this  way. 

Phenyl  hydrazine  is  of  extreme  importance  in  the  chemistry  of  the 
sugars  for  the  separation,  recognition,  and  transformation  of  the  dif- 
ferent varieties  of  the  sugars.  Without  this  reagent,  the  fundamental 
explanations  of  the  last  few  years  in  this  field  could  scarcely  have  been 
made.  If  one  molecule  of  phenyl  hydrazine  is  allowed  to  act  on  one 
molecule  of  a  sugar,  a  normal  hydrazone  is  formed,  e.g. : 

CH2.OH(CH.OH)4.CHO  +  C6H5.NH.NH2 

Grapesugar         =  CH2<  OH(CH  .  OH)4  .  CH  +  H2O 

N-NH.CgH,, 

But  if  the  phenyl  hydrazine  is  used  in  excess,  it  acts  as  an  oxidising 
agent  toward  the  sugar,  extracting  water,  e.g.,  in  the  above  case, 
one  of  the  secondary  alcohol  (CH.OH)  groups  adjoining  the  alde- 
hyde (CHO)  group  is  oxidised  to  a  ketone  group,  which  again  reacts 
with  the  hydrazine.  The  compound  thus  obtained  is  called  an  "Osa- 
zone."  In  the  above  example,  there  is  obtained  a  compound  of  this 
composition : 

CH2.OH.(CH.OH)3.C— CH=N.NH.C6H5 

N 
NH.C6H5 


AROMATIC   SERIES  255 

If  this  compound  is  heated  with  hydrochloric  acid,  it  acts  in  the 
same  way  as  all  hydrazones,  and  phenyl  hydrazine  is  eliminated ;  the 
original  unchanged  sugar  is  not  formed  again,  but  an  oxidation  product 
of  it  is  obtained,  a  so-called  "Osone."  In  the  example  selected,  the 
osone  is : 

CH2.OH.(CH.OH)3.CO.CHO. 

If  this  compound  is  treated  with  a  reducing  agent,  the  aldehyde 
group  and  not  the  ketone  group  is  reduced,  and  the  original  sugar  is 
not  obtained : 

CH2.OH(CH.OH)3.CO.CH2.OH. 

The  aldose  is  converted  into  a  ketose,  the  grape  sugar  into  fruit 
sugar.  The  general  importance  of  the  reaction  as  applied  to  the  sugars 
may  be  inferred  from  these  brief  statements. 

EXPERIMENT  :  A  cold  solution  of  2  grammes  of  phenyl  hydrazine 
hydrochloride  and  3  grammes  of  crystallised  sodium  acetate  in 
15  c.c.  of  water  is  treated  with  a  solution  of  i  gramme  of  pure 
grape  sugar  in  5  c.c.  of  water,  and  warmed  on  the  water-bath. 
After  about  10  minutes,  the  fine,  yellow  needles  of  the  osazone 
begin  to  separate  out;  the  quantity  is  increased  by  a  longer 
heating.  After  heating  an  hour,  the  crystals  are  filtered  off, 
washed  with  water,  and  allowed  to  dry  in  the  air.  Melting-point, 

205°. 

Phenyl  hydrazine  undergoes  condensation  with  /?-diketones  and 
/?-ketone-acid-esters  with  the  formation  of  ring  compounds  contain- 
ing nitrogen  —  the  so-called  pyrazoles  and  pyrazolones.  The  phenyl 
methyl  pyrazolone  formed  from  acetacetic  ester  and  phenyl  hydrazine 
is  of  importance : 


CH,.C 


.  CH2  •  CO  OC2H5j  -  CH3  -  C  -  CH2 .  CO  +  H2O  +  C2H5OH 


N-      —  N[HJ.C6H5  N NCCH5 


rom  which,  by  the  action  of  methyl  iodide,  the  important  febrifuge  — 
" Antipyrine "  —  dimethyl  phenyl  pyrazolone  is  obtained: 

CH3.C— CH— CO 
CH3-N N-C6H5 

Antipyrine 


256  SPECIAL  PART 

If  the  primary  hydrazines  are  boiled  with  copper  sulphate,1  or  ferric 
chloride,2  the  hydrazine  radical  is  replaced  by  hydrogen,  and  there  is 
obtained,  e.g.,  from  phenyl  hydrazine,  benzene : 

C6H5.  NH .  NH2  +  2  CuO  =  C6H6  +  N2  +  H2O  +  Cu2O, 
or  C6H5.NH.NH2  + CuO     =  C6H6  +  Na  +  H8O  +  Cu. 

The  statements  made  above  concerning  the  replacement  of  a  diazo- 
group  by  hydrogen  are  also  applicable  to  this  reaction.  If  it  is  desired 
to  prepare  an  amido-compound  from  an  amido-free  compound,  and  if 
the  direct  reduction  of  the  diazo-compound  by  sodium  stannous  oxide 
or  alcohol  (see  page  237)  has  been  shown  to  be  impracticable,  then,  as 
above,  the  hydrochloric  acid  salt  of  the  corresponding  hydrazine  is  pre- 
pared, the  free  hydrazine  is  liberated,  and  oxidised  with  caustic  soda. 
The  amido-free  substance  is  not  always  easily  volatile,  as  in  the  example 
cited.  In  a  case  of  this  kind,  the  oxidation  may  be  effected  in  an  open 
vessel ;  the  reaction  product  is  obtained  either  by  filtering  or  by  extract- 
ing with  ether.  It  may  be  pointed  out  here  that  it  is  more  convenient  to 
separate  the  hydrazine  from  the  hydrochloric  acid  salt,  and  subject  this 
to  oxidation.  If  a  hydrochloric  acid  salt  of  a  hydrazine  is  oxidised,  it 
may  happen  that  the  hydrazine  radical  will  be  replaced  by  chlorine : 

C6H5.NH .NH2,  HC1  +  O2  =C6H5.C1  +  N2  +  2 H2O, 
which  may  give  rise  to  complications. 

12.  REACTION:  (a)  PREPARATION  OP  AN  AZO  DYE  FROM  A  DIAZO- 
COMPOUND  AND  AN  AMINE.  (&)  REDUCTION  OF  THE  AZO-COM- 
POUND 

EXAMPLES  :   (a)  Helianthine  from  Diazotised  Sulphanilic  Acid  and 

Dimethyl  Aniline 
(£)  Reduction  of  Helianthine 

(a)  Dissolve  10  grammes  of  sulphanilic  acid,  dried  on  the 
water-bath,  in  a  solution  of  3.5  grammes  of  dehydrated  sodium 
carbonate  in  150  c.c.  of  water,  and  treat  with  a  solution  of  4.2 
grammes  of  pure  sodium  nitrite  in  20  c.c.  of  water.  To  rhis 
mixture,  after  being  cooled  by  water,  is  added  a  quantity  of 
hydrochloric  acid  solution  corresponding  to  2.5  grammes  of  an- 

i  B.  18, 90.  2  B.  18,  786. 


AROMATIC  SERIES 


257 


hydrous  hydrochloric  acid.  For  this  purpose,  concentrated  hydro- 
chloric acid  is  diluted  with  an  equal  volume  of  water,  and  the 
specific  gravity  of  the  dilute  acid  is  determined  by  a  hydrometer. 
Consult  a  table,  to  find  the  amount  of  anhydrous  hydrochloric 
acid  corresponding  to  the  reading  of  the  hydrometer.  (See 
Graham-Otto,  Vol.  II  i,  p.  SiS.)1 

Before  diazotising  the  sulphanilic  acid,  a  solution  of  7  grammes 
of  dimethyl  aniline  in  the  theoretical  amount  of  hydrochloric  acid 
is  prepared.  Aromatic  bases  cannot  be  neutralised  with  hydro- 
chloric acid  in  the  same  way  as  caustic  potash,  caustic  soda, 
and  ammonium  hydroxide,  by  gradually  treating  with  the  acid  and 
testing  with  blue  litmus-paper  until  the  liquid  is  just  acid.  In  con- 
sequence of  the  weak  basic  character  of  the  amines,  their  hydro- 
chlorides  still  give  an  acid  reaction  with  blue  litmus-paper,  there- 
fore an  acid  reaction  can  be  obtained  even  at  the  beginning  of 
the  neutralisation.  Red  fuchsine-paper  possesses  the  property  of 
becoming  decolourised  by  free  hydrochloric  acid,  which  converts 
the  red  monoacid  fuchsine  into  a  colourless  polyacid  salt.  The 
hydrochloric  acid  salts  of  bases,  on  the  contrary,  do  not  produce 
this  decolourisation.  In  order  to  neutralise  the  dimethyl  aniline 
(7  grammes),  it  is  treated  with  25  c.c.  of  water,  and,  with  stirring, 
small  quantities  of  concentrated  hydrochloric  acid  are  added; 
after  each  addition  a  test  is  made  to  show  whether  or  not  the 
fuchsine-paper  is  decolourised. 

The  dimethyl  aniline  hydrochloride  thus  obtained  is  added  to 
the  diazo-solution,  and  the  mixture  is  made  distinctly  alkaline  by 
the  addition  of  not  too  much  caustic  soda  solution.  The  dye 
separates  out  directly;  the  quantity  can  be  increased  if  25 
grammes  of  finely  pulverised  sodium  chloride  are  added  to  the 
solution.  After  filtering  off  and  pressing  out  on  a  porous  plate, 
the  dye  is  recrystallised  from  a  little  water. 

1  If  the  specific  gravity  of  the  hydrochloric  acid  has  been  determined,  the  per- 
centage of  free  anhydrous  acid  may  be  found  without  a  table,  by  the  following 
calculation :  The  decimal  number  is  multiplied  by  2,  and  a  decimal  point  placed 
after  the  first  two  figures  thus  obtained,  e.g.,  sp.  gr.  =  1.134;  2X134  =  268. 
Percentage  contents  =  26.8.  If  the  sp.  gr.  is  greater  than  1.18,  a  table  must  be 
consulted. 

s 


258  .SPECIAL   PART 

Preparation  of  Fuchsine- Paper :  A  crystal  of  fuchsine,  the  size 
of  a  lentil,  is  pulverised,  dissolved  by  heating  in  100  c.c.  of  water, 
and  the  solution  filtered. 

Into  this  immerse  strips  of  filter-paper  2  cm.  wide ;  they,  are 
dried  either  by  suspending  from  a  string  in  an  acid-free  place, 
or  on  the  water-bath.  The  paper  must  not  be  an  intense  red, 
but  only  a  faint  rose  colour.  If  the  colour  is  too  intense,  the 
fuchsine  solution  must  be  correspondingly  diluted  with  water. 

Instead  of  the  fuchsine-paper,  the  commercial  Congo-paper  will 
serve,  the  red  colour  of  which  is  changed  to  blue  by  free  acid. 

(^)  Dissolve  2  grammes  of  the  dye  in  the  least  possible  amount 
of  water  by  heating ;  while  the  solution  is  still  hot,  treat  with  a 
solution  of  8  grammes  of  stannous  chloride  in  20  grammes  of 
hydrochloric  acid  until  decolourisation  takes  place.  The  colour- 
less solution  is  then  well  cooled,  upon  which,  especially  if  the 
sides  of  the  vessel  are  rubbed  with  a  glass  rod,  sulphanilic  acid 
separates  out :  it  is  filtered  off  through  asbestos  or  glass-wool. 
The  filtrate  is  diluted  with  water,  and  caustic  soda  solution  is 
added  until  the  oxyhydrate  of  tin  separating  out  at  first  is  again 
dissolved.  It  is  then  extracted  with  ether  several  times,  the 
ethereal  solution  dried  with  potash,  and  the  ether  evaporated, 
upon  which  the  p-amidodimethyl  aniline  remains  as  an  oil :  on 
cooling  and  rubbing  with  a  glass  rod,  it  solidifies. 

Reactions  of  p-Amidodimethyl  Aniline  :  1  The  amidodimethyl 
aniline  is  treated  gradually  with  small  quantities  of  dilute  sul- 
phuric acid  until  it  is  just  dissolved.  Add  a  few  drops  of  this 
solution  to  a  dilute  solution  of  hydrogen  sulphide  in  a  beaker 
which  has  been  treated  with  -£$  of  its  volume  of  concentrated 
hydrochloric  acid.  To  this  mixture  now  add  several  drops  of  a 
dilute  solution  of  ferric  chloride.  An  intensely  blue  colouration, 
due  to  the  formation  of  methylene  blue,  takes  place. 

Diazo-compounds  react  with  amines,  as  well  as  phenols,  to  form  the 
Azo  dyes :  2 

1  B.  16,  2235.  2  A.  137,  60 ;  B.  3,  233. 


AROMATIC   SERIES  259 

(1)  C6H5  .  N2  .  Cl  +  C6HS  .  N(CH3)2 

=  CfiH5  .  N=N  .  C8H4  .  N(CH3)2  +  HC1 

Dimethylamidoazo  benzene 

(2)  C6H5  .  N2  .  Cl  +  C6H5  .  OH  =  C6H5  .  N=N  .  C6H4  .  OH  +  HC1 

(In  presence  of  alkali)  Oxyazo  benzene 

According  to  Hantzsch  the  reaction   takes  place  in  the   following 
manner  : 

CCH5        CCH4.OH      C6H5C6H4OH    CCH5 


N=N  + 


=  N:=:N 


Cl  H  CCH4.OH 

An  unstable  syn-azo  compound  is  formed  first,  which  rapidly  changes 
into  the  more  stable  anti-azo  compound. 

In  accordance  with  these  two  typical  reactions,  the  vast  number  of 
monoazo  dyes  are  prepared.  The  great  number  of  possible  combina- 
tions can  be  inferred  from  the  following  considerations :  In  reaction 
(i),  instead  of  diazotised  aniline,  other  bases,  like  o-toluidine,  p-tolui- 
-  dine,  xylidine,  cuminidine,  a-naphthyl  amine,  /?-naphthyl  amine,  etc., 
may  be  used.  In  addition,  the  most  varied  derivatives  of  these  bases, 
especially  their  sulphonic  acids,  like  sulphanilic  acid,  metanilic  acid, 
the  large  number  of  a-  and  /3-naphthyl  amines  mono-  to  poly-sulphonic 
acids,  may  also  be  employed.  Instead  of  dimethyl  aniline,  the  diazo- 
compound  can  be  combined  or  "  coupled  "  with  other  tertiary,  and  in 
part  also  with  secondary  and  primary  amines,  like  diphenyl  amine,  or 
m-diamines,  etc.  In  the  second  reaction,  the  diazo-compounds  of  the 
just  mentioned  bases  can  be  employed  as  the  starting-point,  and  these 
can  be  combined  with  mon-acid  phenols,  like  cresol,  naphthols,  or  di- 
acid  phenols  like  resorcinol,  or  the  sulphonic  acids  of  these  phenols, 
especially  the  numerous  sulphonic  acids  of  both  naphthols.  Since  a  dye 
must  be  soluble  in  water,  and  the  alkali  salts  of  the  sulphonic  acids  of  the 
dyes  are  more  easily  soluble  than  the  mother  substance  containing  no 
sulphonic  acid  groups,  therefore,  in  the  preparation  of  the  azo  dyes,  the 
starting-point  is  usually  a  sulphonic  acid.  A  few  examples  will  explain 
these  statements : 

I.    A  mi  do  azo  Dyes 

/SO.H 

p-C6H/  .C(;H4.N(CH3)2  =  Helianthine, 

Diazotised  sulphanilic  acid  +  dimethyl  aniline 

.  C6H4 .  NH  .  CCH5  =  Metanilic  Yellow, 

Diazot.     Metanilic  acid  +•  diphenylamine     (secondary  base) 

/NH. 

C,Hr.N=N.CKH.{<  =  Chrysoidine. 

\NH? 

Diazot.     Aniline  +  m-phenylenediamine        (primary 'base1! 


26O  SPECIAL   PART 

II.    Oxyazo  Dyes 

/S03H 

p-C6H/  . C10H6. OH  =  Orange  II., 

>NzzN 

Diazot.     Sulphanilic  acid  +  £-naphthol 

/S03H 
C10H,/  . C10H6. OH  =  Fast  Red  (first  red  azo  dye)? 

\NzzN 

Diazot.     a-Naphthionic  acid  +  |3-naphthol 

/OH 

C6H5 .  N=N .  C10H  /  =  Croceine  Orange, 

\SO3H 

Diazot.     Aniline  +  croceine  acid 
(/3-Naphthol  sulphonic  acid) 

/OH 

(CH3)2.C6H3.N=N.C10H/  =  Xylidine  Ponceau. 

\(S03H)2 

Diazot.     Xylidine  +  |3-naphthol  disulphonic  acid 

Concerning  the  constitution  of  the  azo  dyes,  provided  the  com- 
ponents are  known,  the  only  question  to  solve  is :  which  hydrogen 
atom  of  the  undiazotised  component  combines  with  the  acid  radical  of 
the  diazo-compound  (the  acid  thus  formed  being  eliminated).  The 
question  may  be  answered  by  investigating  the  reduction  products  of 
the  azo  dyes.  By  energetic  reduction,  best  in  acid  solution  with  stan- 
nous  chloride,  the  double  NuiN  union  is  broken  up,  thus  forming,  with 
the  addition  of  4  atoms  of  hydrogen,  two  molecules  of  a  primary 
amine,  e.g. : 

/S03H  /S03H  /NH2 

C6H/  .CGH4.N(CH3)2  +  2H2  =  C6H/  +  C6H/ 

\N=N  \NH2  \N(CH3)2 

From  this  equation  it  is  evident  that  by  reduction,  the  amine  which 
was  diazotised  —  in 'the  above  case  sulphanilic  acid  —  may  be  obtained 
again  on  the  one  hand,  on  the  other  an  amido-group  is  introduced  into 
the  second  component.  If  the  constitution  of  this  second  product  can 
be  determined,  then  the  constitution  of  the  azo  dyes  is  also  determined. 
It  may  be  stated  as  a  general  rule  that,  when  a  diazo-compound  com- 
bines with  an  amine  or  phenol,  the  hydrogen  atom  in  the  para  position 
to  the  amido-  or  hydroxyl-group  is  always  substituted.  In  accordance 
with  this,  in  the  above  case,  p-amidodimethyl  aniline  ought  to  be 
obtained  on  reduction.  If  the  para  position  is  already  occupied,  then 
the  o-hydrogen  atom  unites  with  the  acid  radical. 


AROMATIC   SERIES  26 1 

In  some  cases,  the  formation  and  consequent  reduction  of  an  azo 
dye  with  the  introduction  of  an  amido-group  into  a  phenol  or  amine  is 
of  practical  value. 

Azo  dyes  which  contain  two  "  chromophore  groups,"  NzzN,  and 
which  are  called  dis-  or  tetr-azo  dyes,  can  be  prepared ;  two  methods 
may  be  employed :  (i)  The  starting-point  is  an  amido-azo-compound 
which  already  contains  one  azo  group;  this  is  diazotised,  and  then 
united  with  an  amine  or  phenol.  "  Biebrich  scarlet"  is  obtained  in 
this  way,  by  diazotising  the  disulphonic  acid  of  amidoazobenzene,  and 
combining  it  with  /3-naphthol : 

0H 


Diazot.     Amidoazobenzene  disulphonic  acid  +  /3-naphthol 

(2)  A  diamine  is  the  starting-point ;  this  is  diazotised,  and  the  bisdiazo- 
compound  is  combined  with  two  molecules  of  an  amine  or  phenol. 
To  this  class  belong  the  important  dyes  of  the  Congo  group,  prepared 
from  the  benzidine  bases  (see  page  231),  e.g. : 

/NH2 
C6H4-N=N-C]0H/ 


Diazot.     Benzidine  +  2  mol.  a-naphthionic  acid 

)H 

^TO.OH  =  chrysamine. 

6H4.N=N.C6H/ 
— *—  \CO.OH 


Diazot.     Benzidine  +  2  mol.  salicylic  acid 

These  Congo  dyes  possess  the  noteworthy  property  of  colouring 
vegetable  fibres  (cotton)  directly,  whereas,  with  almost  all  other  azo 
dyes,  the  cotton  must  be  mordanted  before  dyeing. 

In  conclusion,  the  above  dye-stuff  reaction  (which  may  be  used  for 
detecting  the  smallest  amount  of  hydrogen  sulphide)  is  technically 
carried  out  on  the  large  scale,  for  the  manufacture  of  the  important 
methylene  blue.  The  reaction  takes  place  as  follows  :  From  two  mole- 
cules of  the  diamine  there  is  split  off  on  oxidation  with  ferric  chloride. 


262  SPECIAL   PART 

one  molecule  of  ammonia,  while  a  derivative  of  diphenyl  amine  is 
formed  : 

XN(CH3)2         /N(CH3)2 

C6H4 


\N(CH3)2 

In  the  presence  of  hydrogen  sulphide  and  hydrochloric  acid,  there 
is  formed  from  this,  by  the  oxidising  action  of  ferric  chloride,  a  deriva- 
tive of  thiodiphenylamine,  as  follows  : 


N(CH3) 


/N(CHS), 

lH3> 

TJ   / 


Methylene  blue 

l_+0- 

13.    REACTION:    PREPARATION  OF  A  DIAZOAMIDO-COMPOUND 

EXAMPLES:  Diazoamidobenzene  from  Diazobenzenechloride  and 

Aniline l 

Dissolve  10  grammes  of  freshly  distilled  aniline  in  a  mixture 
of  100  c.c.  of  water,  and  that  quantity  of  concentrated  hydro- 
chloric acid  corresponding  to  1 2  grammes  anhydrous  hydrochloric 
acid  (determine  the  sp.  gr.  by  a  hydrometer).  The  solution  is 
cooled  with  ice-water,  and  diazotised  with  a  solution  of  8  grammes 
of  sodium  nitrite  in  50  c.c.  of  water,  in  the  manner  already  de- 
scribed. A  solution  containing  10  grammes  of  aniline,  50  grammes 
of  water,  and  the  exact  theoretical  amount  of  hydrochloric  acid  is 
previously  prepared  according  to  the  directions  given  on  pages 


i  A.  121,  257. 


AROMATIC   SERIES  263 

256  and  257  ;  this  is  well  cooled  with  ice  water,  and  added  to  the 
diazo-solution,  with  stirring.  Further,  50  grammes  of  crystallised 
sodium  acetate  are  dissolved  in  the  least  possible  amount  of  water, 
the  cooled  solution  is  added,  with  stirring,  to  the  mixture  of  the 
diazo-compound  with  aniline  hydrochloride.  After  standing  half  an 
hour,  the  diazoamidobenzene  separates  out,  and  is  filtered  off  with 
suction,  washed  several  times  with  water,  well  pressed  out  on  a 
porous  plate,  and  recrystallised  from  ligroin.  Melting-point,  98°. 
Yield,  almost  theoretical. 

If  one  molecule  of  a  diazo-compound  is  allowed  to  act  on  one  mole- 
cule of  a  primary  amine,  the  acid  radical  of  the  former  unites  with  the 
hydrogen  atom  of  the  latter,  upon  which  the  organic  residues  combine, 
as  in  the  formation  of  the  azo  dyes.  In  this  case,  an  amido-hydrogen 
atom  is  eliminated,  so  that  a  compound  containing  a  chain  of  three 
nitrogen  atoms  is  formed ;  in  the  formation  of  an  azo  dye,  one  of  the 
benzene-hydrogen  atoms  of  the  amine  is  eliminated : 

C6H5.  N2.C1  +  C6H5.  NH2  =  C6H5.  N=N .  NH  .C6H5  +  HC1 

Diazoamidobenzene 

Mixed  diazo-compounds  may  also  be  prepared  by  causing  the  diazo- 
derivative  of  an  amine  to  combine  with  another  amine : 

/CH3 
C6H5 .  N, .  Cl  +  C6H/  =  C6H5 .  N=N .  NH .  C6H4 .  CH3  +  HC1 

\Nri2 

Benzenediazoamidotoluene 

Diazo-compounds  combine  only  with  the  free  amines  to  form  diazo- 
amido  compounds ;  the  object  of  the  addition  of  sodium  acetate  at  the 
end  of  the  reaction  (see  above)  is  to  set  free  the  base  from  aniline 
hydrochloride. 

The  diazoamido-compounds  are  yellow  substances  which  do  not  dis- 
solve in  acids.  They  are  far  more  stable  than  the  diazo-compounds, 
and  may  be  recrystallised  without  decomposition.  Still,  if  they  are 
heated  rapidly  they  puff  up  suddenly  and  decompose.  In  their  reac- 
tions they  behave  like  a  mixture  of  a  diazo-compound  and  an  amine. 
If,  e.g.,  they  are  boiled  with  hydrochloric  acid,  they  decompose  with 
evolution  of  nitrogen,  and  form  a  phenol  and  an  amine  : 


264  SPECIAL   PART 

On  heating  with  cuprous  chloride  and  hydrochloric  acid,  the  Sand- 
meyer  reaction  takes  place : 

C6H5.  N=N  .  NH .  C6H5  +  HC1  =  C6H- .  Cl  +  C6H5 .  NH2  +  N2 
By  reduction  with  acetic  acid  and  zinc  dust,  they  form  a  hydrazine : 
C6H5.N=N.NH.C(JH5  +  2  H2  =  C(,H,.NH  .  NH2  +  C6H5.  NH2 

But,  in  addition  to  the  reaction-product  of  the  diazo-radical,  there  is 
always  formed  one  molecule  of  an  amine. 

Under  the  influence  of  nitrous  acid,  they  decompose,  the  amine 
residue  being  diazotised,  into  two  molecules  of  a  diazo-compound : 

C6H5 .  NziN .  NH  .  C,H5  +  HNO2  +  2  HC1  =  2  C6H5 .  N2 .  Cl  +  2  H2O 

If  a  diazcamido-compound  is  warmed  with  an  amine  in  the  presence 
of  some  amine  hydrochloride,  transformation  to  the  isomeric  amidoazo- 
compound  takes  place  : 

C6H5 .  N=N .  NH  .  CBHa  =  C6H5 .  N  ~N  .  C6H4 .  NH2 

Amidoazobenzene 

The  next  preparation  deals  with  this  reaction. 

The  diazo-compounds  also  have  the  power  of  combining  with  sec- 
ondary amines  to  form  diazoamido-compounds,  —  the  combinations 
with  an  alkaloid  base,  piperidine  C.HUN  : 

CH2 

H2C/\CH5 
H2Cl      JCH, 


NJ 

are  of  especial  value  for  preparations.  If  they  are  gradually  warmed 
with  hydrofluoric  acid,  they  are  decomposed  with  the  evolution  of  nitro- 
gen into  piperidine  and  a  fluoride  : 1 

C6H5.Nz=N.N.C5H10  +  HF1  =  CGH-.F1  +  C5HUN  +  N2 

Benzenediazopiperidine  Fluorbenzene 

In  this  way  it  has  been  possible  to  prepare  the  aromatic  fluorides. 

In  accordance  with  the  older  views  it  was  believed  that  the  aromatic 
fluorides  could  not  be  obtained  from  the  diazo-compounds  in  the  same 
way  in  which  the  analogous  chlorides,  bromides,  and  iodides  are  pre- 
pared ;  recently  however  they  have  been  obtained  by  the  direct  decom- 
position of  the  diazo-fluorides. 


243,  239. 


AROMATIC   SERIES  265 


14.  REACTION:    THE   MOLECULAR   TRANSFORMATION   OF  A  DIAZO 
AMIDO-COMPOUND  INTO  AN   AMIDOAZO-COMPOUND 

EXAMPLE  :   Amidoazobenzene  from  Diazoamidobenzene 

To  a  mixture  of  10  grammes  of  crystallised  diazoamidobenzene, 
finely  pulverised,  and  5  grammes  of  pulverised  aniline  hydro- 
chloride,  contained  in  a  small  beaker,  add  25  grammes  of  freshly 
distilled  aniline  ;  the  mixture  is  then  heated,  with  frequent  stirring, 
one  hour,  on  the  water-bath,  at  45°.  It  is  then  transferred  to  a 
larger  vessel,  and  treated  with  water ;  dilute  acetic  acid  is  added, 
until  all  the  aniline  has  passed  into  solution,  and  the  undissolved 
precipitate  remaining  is  completely  solid.  This  is  filtered  off, 
washed  with  water,  heated  in  a  large  dish  with  a  large  quantity 
of  water  (about  a  litre),  and  gradually  treated  with  hydrochloric 
acid  until  the  greatest  portion  of  the  precipitate  is  dissolved. 
From  the  filtered  solution,  steel-blue  crystals  of  amidoazobenzene 
hydrochloride  separate  out,  on  long  standing ;  these  are  filtered 
off,  and  washed  with  dilute  hydrochloric  acid,  not  with  water. 

If  aniline  hydrochloride  is  not  at  hand,  prepare  it  by  adding 
aniline  to  concentrated  hydrochloric  acid,  with  stirring.  After 
cooling,  the  pasty  mass  of  crystals  separating  out  is  filtered  on 
glass-wool,  pressed  firmly  together  on  the  filter  with  a  pestle,  and 
then  spread  in  thin  layers  on  a  porous  plate. 

In  order  to  obtain  the  free  amidoazobenzene,  the  hydrochloride 
is  warmed  with  dilute  ammonia,  the  free  base  filtered  off,  dis- 
solved in  alcohol  by  heating,  and  hot  water  is  added  until  the  liquid 
begins  to  be  turbid.  Melting-point,  1 2  7-1 28°.  Yield,  6-8  grammes. 

If  a  diazoamido-compound  is  heated  with  an  amine  and  some  amine 
hydrochloride,  it  goes  over  to  an  amidoazo-compound.  The  most 
probable  cause  of  the  reaction  is  that  the  amine  residue  of  the  diazo- 
amido-compound unites  with  a  benzene-hydrogen  atom  of  the  amine 
hydrochloride,  upon  which  the  diazo-residue  unites  with  the  residue 
of  the  amine  salt  to  form  amidoazobenzene : 

C6H5 .  N=N .  |NH  .  QH,  +  H  i . C,.H4 .  NH2 

""=  C6H ,.  N  —  N .  C6H4 .  NH2  +  C6H5 .  NHa 

Amidoazobenzene 


266  SPECIAL   PART 

While  the  amidoazobenzene  does  not  unite  with  hydrochloric  acid, 
the  new  molecule  of  the  amine  formed  in  the  reaction  does,  and  thus 
there  is  a  molecule  of  the  amine  hydrochloride  present,  which  again 
causes  the  transformation,  so  that  a  small  amount  of  the  hydrochloride 
may  transform  an  indefinitely  large  amount  of  the  diazoamido-compound. 

If  amidoazobenzene  is  reduced,  p-phenylene  diamine  and  aniline  are 
obtained.  The  transformation  accordingly  results  in  the  formation  of 
a  compound  in  which  the  amido-groups  are  in  the  para  position,  which 
always  happens  when  the  para  position  is  unoccupied.  The  amidoazo- 
compounds  possess  weakly  basic  properties ;  but  if  their  salts  are 
treated  with  much  water,  they  partially  dissociate. 

The  amidoazobenzene  hydrochloride  came  into  the  market  formerly, 
as  a  yellow  dye,  under  the  name  of  "Aniline  Yellow."  At  present,  it 
is  scarcely  used,  but  there  is  prepared  from  it,  by  heating  with  sulphuric 
acid,  a  mono-  or  di-sulphonic  acid,  which  in  the  form  of  its  alkali  salts 
finds  application  as  a  dye  under  the  name  of  "  Acid  Yellow,"  or  "  Fast 
Yellow."  As  already  mentioned  under  the  dis-azo  dyes,  from  the 
diazo-compound  of  this  dye,  "  Biebrich  Scarlet"  may  be  made  by  com- 
bination with  /?-naphthol.  Finally,  the  amidoazobenzene  is  still  used 
for  the  preparation  of  the  Induline  dyes. 


15.   REACTION:   OXIDATION  OF  AN   AMINE  TO   A  QUINONE 
EXAMPLE  :    Quinone  from  Aniline l 

To  a  solution  of  25  grammes  of  aniline  in  a  mixture  of  200 
grammes  of  concentrated  pure  sulphuric  acid  and  600  c.c.  of  water 
contained  in  a  thick-walled  beaker  (a  small  battery  jar),  cooled 
to  5°  by  being  surrounded  with  ice,  add  gradually,  with  constant 
stirring  (use  a  small  motor),  from  a  dropping  funnel,  a  solution  of 
25  grammes  of  sodium  dichromate  in  100  c.c.  of  water  (Fig.  69). 
Should  the  temperature  rise  above  10°,  the  addition  of  the  dichro- 
mate must  be  discontinued  for  a  short  time  and  a  few  pieces  of  ice 
thrown  into  the  beaker.  The  reaction-mixture  is  then  allowed  to 
stand  over  night  in  a  cool  place,  and  the  next  morning  it  is  again 
cooled  and  stirred,  while  a  solution  of  50  grammes  of  sodium  di- 
chromate in  200  c.c.  of  water  is  added.  After  the  mixture  has  been 
allowed  to  stand  until  midday,  it  is  divided  into  two  equal  parts,  one 
of  which  is  worked  up  into  quinone  as  follows  :  In  -a  large  separating 

*  A.  27,  268;  45,354;  215, 125;  B.  19, 1467;  20,  2283. 


AROMATIC   SERIES 


267 


funnel  one  half  is  treated  with  |  its  volume  of  ether,  and  the  two 
layers  thus  formed  are  carefully  shaken  together.  If  the  shaking 
is  too  vigorous,  the  layers  will  not  readily  separate.  After  allowing 
it  to  stand  for  half  an  hour,  the  lower  layer  is  run  off  (see  page 
44,  Separation  of  coloured  liquids),  the  ethereal  solution  is  filtered 
through  a  folded  filter,  and  the  ether  distilled  off  (water-bath  with 
warm  water).  The  water  solution  is  again  extracted  with  the  con- 
densed ether,  and  the  ether  again  distilled  from  the  same  flask  as 
before.  In  order  to  obtain  perfectly  pure  quinone,  a  rapid  current 
of  steam  is  passed  over  the  crude  product  —  it  is  not  treated  with 


FIG.  69. 

water  ;  the  pure  quinone  is  carried  over  with  the  steam  to  the 
condenser  and  receiver,  where  it  crystallises  in  the  form  of  golden- 
yellow  needles ;  they  are  filtered  off  and  dried  in  a  desiccator. 
Melting-point,  116°.  Yield,  10-12  grammes. 

If  sodium  dichromate  is  not  at  hand,  the  potassium  salt  may  be 
used  for  the  oxidation.  In  this  case,  25  grammes  of  aniline  are 
dissolved  in  a  mixture  of  200  grammes  of  sulphuric  acid  and  800 
c.c.  of  water ;  then  add,  as  above,  with  stirring  and  good  cooling, 
25  grammes  of  potassium  dichromate,  powdered  extremely  fine. 
On  the  next  day  add  50  grammes  of  this  salt.  In  other  respects, 
proceed  as  above. 

For  the  preparation  of  hydroquinone  from  quinone  see  p.  270. 

Many  primary  aromatic  amines  yield  quinones  on  oxidation  with 
chromic  acid.  But  the  reaction  cannot  be  expressed  in  a  simple  equa- 
tion ;  still,  it  is  always  true  that  the  amido-group  and  the  hydrogen 


268  SPECIAL   PART 

atom  in  the  para  position  to  this  are  each  replaced  by  an  oxygen 
atom,  e.g.  : 

C6HS.NH2—  ^C6H,02 

Quinone 

,CH3 
o-C6H4<          - 

\NH2  O 

Toluidine  Tolyl  quinone 

The  tendency  to  form  quinones  is  so  great  that  even  in  cases  where  the 
para  position  to  the  amido-group  is  occupied  by  an  alkyl  (methyl)  radical, 
the  latter  is  split  offand  a  quinone  (poorer  in  carbon  contents)  is  formed. 
Indeed,  in  the  simplest  cases,  like  p-toluidine  and  asym.  m-xylidine,  the 
reaction  is  very  incomplete  ;  however,  mesidine,  as  well  as  pseudocumidine, 
give  satisfactory  yields  of  quinones  belonging  to  the  next  lower  series  : 

NH  O 


H,C—  /-CH 


H3C- 


:HS  o 

Pseudocumidine  p-Xyloquinone 

But  if  the  para  position  is  occupied  by  an  amido-,  oxy-,  or  sulphonic 
acid-group,  this  is  eliminated  and  a  quinone  formed : 


P-C6H/ 


NH 


, 
X 


From  these  methods  of  formation  it  follows  that  the  two  quinone- 
oxygen  atoms  are  in  the  para  position  to  each  other.  The  quinone 
reaction  can  be  used  in  doubtful  cases  to  decide  whether  a  compound 


AROMATIC   SERIES 


269 


belongs  to  the  para  series.  The  quinones  can  also  be  obtained  very 
easily  from  p-dioxy-compounds  as  well  as  from  the  p-sulphonic  acids 
of  mon-acid  phenols : 

p-C6H/        +  O  =  C6H402  +  H20 
X)H 

/OH 

p-C6H/  _^c6H402- 

XSO3H 

Two  formulae  for  the  quinones  have  been  proposed:  — 


According  to  the  former  the  quinones  still  contain  the  true  benzene 
ring  with  either  three  double  or  six  centric  bonds.  The  two  oxygen 
atoms  are  only  singly  united  with  the  benzene-carbon  atoms,  and  are 
united  to  each  other.  According  to  the  second  formula,  the  quinones 
do  not  contain  the  true  benzene  ring,  but  they  are  derived  from  a 
dihydrobenzene, 

H      H 


H 


and  are  regarded  as  the  di-ketone  derivative  of  this.  According  to 
this  conception,  the  oxygen  atoms  are  connected  by  two  bonds,  as  in 
the  ketones,  with  the  carbon  atoms  of  the  benzene  nucleus.  The  facts 
in  favour  of  the  first  formula  are  these  :  In  many  reactions  both  of  the 


27O  SPECIAL  PART 

oxygen  atoms  are  replaced  by  two  univalent  atoms  or  radicals.  Thus, 
e.g.,  by  the  action  of  phosphorus  pentachloride  on  quinone,  p-dichlor- 
benzene  is  formed,  while  the  second  formula  would  lead  one  to  expect 
a  tetra-chloride.  In  support  of  the  second  formula  is  the  fact  that 
hydroxylamine  acts  directly  on  quinones,  as  on  ketones,  with  the 
formation  of  a  mono-  or  di-oxime. 

The  p-quinones  are  coloured  compounds,  possessing  a  characteristic 
odour ;  they  are  easily  volatile  with  steam,  but  with  a  slight  decomposi- 
tion. They  are  somewhat  volatile  even  with  the  vapour  of  ether,  as 
one  observes  in  the  preparation  of  quinone.  On  reduction  they  take 
up  two  hydrogen  atoms  and  pass  over  to  hydroquinones.  (See  the 
next  preparation)  e.g. : 

/OH 
C6H4O2  +  H2  —  C6H4\ 

\OH 

Hydroquinone 

Of  late  years  ortho-benzoquinone  has  also  been  prepared  by  the 
oxidation  of  pyrocatechin  (o-dihydroxy  benzene)  with  silver  oxide.1 
Under  certain  conditions  a  c&lourless*  o-quinone  is  first  formed,  but 
being  very  unstable  it  passes  over  into  red  quinone.  For  the  colourless 
quinone  the  so-called  Peroxide  formula  has  been  proposed,  and  for  the 
red  quinone  the  Ketone  formula : 


UU 

Colourless  Red 

The  o-quinones  are  less  stable  than  the  p-quinones.     They  are  odour- 
less, and  non-volatile  with  steam. 


16.    REACTION:  REDUCTION   OF    A  QUINONE  TO  A   HYDROQUINONE 
EXAMPLE  :    Hydroquinone  from  Quinone 

Conduct  sulphur  dioxide  into  the  second  half  of  the  quinone 
solution  obtained  above,  until  the  liquid  smells  intensely  of  the 
gas,  then  allow  it  to  stand  for  1-2  hours.  Should  the  odour  of 
sulphur  dioxide  vanish,  it  is  passed  in  again  and  the  mixture 
allowed  to  stand  for  some  time  as  before.  It  is  then  extracted 
with  the  ether  distilled  from  the  quinone  in  the  preceding  experi- 

l B.  37,  4744.  2  B.  41,  2580. 


AROMATIC  SERIES  2/1 

ment,  several  times ;  the  ether  is  evaporated  or  distilled,  and  the 
hydroquinone,  well  pressed  out  on  a  porous  plate,  is  crystallised 
with  the  use  of  animal  charcoal  from  a  little  water.  Melting-point, 
169°.  Yield,  8-10  grammes. 

Since  the  hydroquinone  solution  may  be  extracted  with  ether 
with  much  greater  ease  than  the  quinone  solution,  and  since  the 
hydroquinone  is  smoothly  oxidised  to  quinone,  the  preparation  of 
quinone  may  be  done  as  follows :  The  entire  quantity  of  the  oxi- 
dation product  is  saturated  with  sulphur  dioxide,  and  as  just  de- 
scribed the  hydroquinone  may  be  obtained  by  repeated  extraction 
with  ether.  In  order  to  convert  it  into  quinone  it  is  dissolved  in  the 
least  possible  amount  of  water,  to  which  is  added  2  parts  of  con- 
centrated sulphuric  acid  to  i  part  of  hydroquinone ;  the  well- 
cooled  liquid  is  treated  with  a  water  solution  of  sodium  dichro- 
mate  until  the  green  crystals  of  quinhydrone  (an  intermediate 
product  between  quinone  and  hydroquinone)  separating  out  in 
the  beginning  have  changed  into  pure  yellow  quinone. 

The  equation  for  the  formation  of  hydroquinone  from  quinone  has 
been  given  above.  All  homologous  quinones  react  in  the  same  way. 
The  hydroquinones  are  di-acid  phenols,  which  dissolve  in  alkalies  and 
show  all  the  properties  of  phenols.  They  are  not  volatile  with  steam. 

17.  REACTION:   BROMINATION  OF   AN  AROMATIC  COMPOUND 
EXAMPLE  :  Mono-  and  Di-brombenzene  from  Bromine  and  Benzene 

A  wide-neck  250  c.c.  flask  is  connected  with  a  vertical  tube 
50  cm.  long  and  i^  cm.  wide,  the  upper  end  of  which  is  closed  by 
a  cork  bearing  a  glass  tube,  not  too  narrow,  bent  twice  at  right 
angles.  The-  other  end  is  connected  with  a  flask  containing 
250  c.c.  of  water,  by  a  cork  having  a  small  canal  in  the  side 
(Fig.  70).  The  tube  does  not  touch  the  liquid,  but  the  end  is 
about  i  cm.  above  the  surface.  After  50  grammes  of  benzene1  and 
i  gramme  of  coarse  iron  filings  (the  bromine  carrier)  have  been 
placed  in  the  flask,  it  is  cooled  in  a  large  vessel  (battery  jar)  filled 

1  One  hundred  grammes  of  benzene  should  be  used  if  the  Grignard  reaction 
(see  p.  348)  is  to  be  carried  out  later  on. 


272 


SPECIAL   PART 


with  ice-water  ;  through  the  vertical  tube  there  is  added  40  c.c. 
=  120  grammes  of  bromine:  the  narrow  tube  is  immediately 
connected  with  the  vertical  tube.  After 
some  time  an  extremely  energetic  reaction 
will  begin,  generally  spontaneously,  with  the 
evolution  of  hydrobromic  acid,  which  is 
completely  absorbed  by  the  water.  Should 
the  reaction  not  begin  at  once,  the  ice-water 
is  removed  for  a  short  time,  and  if  necessary 
the  flask  is  immersed  for  a  moment  in 
slightly  warm  water.  But  as  soon  as  even  a 
weak  gas  evolution  begins,  the  flask  is  at 
once  cooled  again,  since  otherwise  the  re- 
action easily  becomes  too  violent.  Should 
this  happen  in  spite  of  the  cooling,  the  cause 
is  found  in  the  fact  that  the  iron  filings  used 
were  too  fine.  In  other  experiments  use 
coarser  filings  or  small  iron  nails.  When 
the  main  reaction  is  over,  the  ice-water  is 
removed,  the  flask  dried  and  heated  over  a 
small  flame  until  the  red  bromine  vapours  are  no  longer  visible 
above  the  dark-coloured  liquid.  The  reaction-product  is  washed 
several  times  with  water  and  then  distilled  with  steam.  As  soon 
as  crystals  of  dibrombenzene  separate  out  in  the  condenser,  the 
receiver  is  changed  and  the  distillation  continued  until  all  the 
dibrombenzene  has  passed  over.  The  liquid  monobrombenzene 
is  separated  from  the  water,  dried  with  calcium  chloride,  and  sub- 
jected to  a  fractional  distillation  ;  the  portion  passing  over  between 
140-170°  is  collected  separately.  This  is  again  distilled,  and  the 
portion  going  over  between  150-160°  collected.  The  boiling-point 
of  the  pure  monobrombenzene  is  155°.  Yield,  60-70  grammes.  The 
residue  boiling  above  1 70°  remaining  in  the  flask  after  the  two  dis- 
tillations, is  poured,  while  still  warm,  on  a  watch-glass,  and  after 
cooling  is  pressed  out,  together  with  the  separately  collected  dibrom- 
benzene, on  a  porous  plate.  On  crystallising  from  alcohol,  coarse 
colourless  crystals  of  p-dibrombenzene  are  obtained,  which  melt 
at  89°. 


FIG.  70. 


AROMATIC  SERIES  2/3 

The  by-product,  hydrobromic  acid,  is  purified  as  described  in 
the  Inorganic  Part.  (See  page  379.) 

A  portion  of  the  hydrogen  of  the  aromatic  hydrocarbons  is  very 
easily  replaced  by  bromine,  especially  in  the  presence  of  a  carrier,  even 
at  low  temperatures  ;  while  in  the  aliphatic  series  the  direct  substitution 
of  bromine  is  not  used  as  a  preparation  method  for  alkyl  bromides, 
the  aromatic  bromides  are  readily  prepared  in  this  way.  According 
to  the  amount  of  bromine  used  one  or  more  hydrogen  atoms  may  be 
substituted ;  it  may  happen,  e.g.,  particularly  with  benzene  under  the 
influence  of  an  energetic  bromination,  that  all  the  hydrogen  atoms  may 
be  replaced  by  bromine.  A  single  bromide,  even  on  using  only  the 
theoretical  amount  of  bromine,  is  never  formed ;  but  rather  a  portion 
of  the  hydrocarbon  is  brominated  short  of  the  theoretical  action,  and 
another  portion  is  always  acted  upon  farther,  with  the  formation  of  a 
higher  bromine  substitution  product.  Thus  in  the  example  above  cited, 
besides  the  principal  product,  monobrombenzene,  a  small  quantity  of 
dibrombenzene  is  formed : 

C6UG  +  Br2    =  C6H5Br  +     HBr 
C6H6  +  2  Br2  =  C6H4Br2  +  2  HBr 

In  most  cases,  however,  the  principal  product  may  be  separated 
from  the  by-product  without  difficulty  by  distillation  or  crystallisation. 
Since  the  hydrogen  atoms  substituted  by  bromine  combine  with  bromine 
to  form  hydrobromic  acid,  therefore,  for  the  introduction  of  each 
bromine  atom,  a  molecule  (two  atoms  of  bromine)  must  be  used. 

The  introduction  of  bromine  can  be  essentially  facilitated  by  the  use 
of  a  so-called  bromine  carrier.  As  such,  the  bromides  of  metalloids, 
or  metals,  are  used;  (i)  either  in  the  already  prepared  condition,  or 
(2)  they  can  be  generated  from  their  elements  in  the  reaction.  To 
the  first  class  belong  ferric  bromide  and  aluminium  bromide.  The 
action  of  ferric  bromide  depends  on  the  fact  that  on  being  reduced  tc 
ferrous  bromide,  it  yields  bromine  in  statu  nascendi: 

FeBr3  =  FeBr2  +  Br. 

Ferric  bromide        Ferrous  bromide 

Since  the  ferrous  bromide  unites  with  bromine  again,  to  form  ferric 
bromide,  a  small  quantity  of  this  has  the  power  to  transfer  an  indefi- 
nitely large  quantity  of  bromine  : 

FeBr2  +  Br  =  FeBr3 . 


2/4  SPECIAL    PART 

Instead  of  ferric  bromide,  ferrous  bromide  or  anhydrous  ferric  chloride 
may  be  used.  The  latter  decomposes  with  hydrobromic  acid  to  ferric 
bromide  and  hydrochloric  acid  : 

FeCl3  +  3  HBr  =  FeBr3  -f  3  HC1. 

The  activity  of  aluminium  bromide  is  explained  by  the  fact  that  it 
unites  with  the  hydrocarbon  to  form  a  double  compound  which  is  more 
capable  of  reacting  with  other  substances  than  the  hydrocarbon  itself. 

To  the  second  class  belong  iodine,  sulphur,  phosphorus,  iron,  alumin- 
ium, etc.  If  these  elements  are  added  to  the  brominating  mixture, 
the  corresponding  bromides  are  formed,  e.g.  : 


While  these  give  up  all  their  bromine,  or  a  portion  of  it,  as  is  the 
case  with  ferric  bromide,  in  the  atomic  condition,  the  residue  again 
unites  with  bromine,  and  as  above,  a  small  quantity  of  the  carrier  may 
transfer  large  quantities  of  atomic  bromine. 

Bromine  can  also  act  on  aromatic  hydrocarbons  to  form  addition 
products,  since  it  may  be  added  in  one,  two,  or  three  molecules,  and 
thus  break  up  the  double  or  centric  union.  Thus,  e.g.,  the  hexabrom- 
addition  product,  C6H6Br6,  is  obtained  from  the  action  of  bromine  on 
benzene  in  the  sunlight.  Since  the  addition  products  render  difficult 
the  purification  of  substitution  products,  especially  on  distillation  (they 
decompose  when  distilled),  it  is  often  necessary  to  remove  them  before 
the  purification,  by  long  boiling  with  alcoholic  caustic  potash,  or  alco- 
holic caustic  soda.  Under  these  conditions,  one-half  of  the  bromine 
atoms  added  in  common  with  the  same  number  of  hydrogen  atoms 
are  abstracted  as  hydrobromic  acid  ;  the  residue  of  the  molecule  is 
converted  into  a  substitution  derivative,  which  is  not  troublesome  in 
the  purification  : 

C6H6Br6  -  C6H8Br8  +  3  HBr. 

On  brominating  benzene,  the  same  products  will  be  formed,  whether 
the  temperature  is  high  or  low,  but  when  its  homologues  are  treated 
with  bromine,  the  nature  of  the  products  depends  upon  the  temperature. 
As  will  be  pointed  out  more  fully,  under  the  chlorination  of  toluene, 
the  law  holds  here,  that  at  low  temperatures  the  halogen  enters  the 
ring  ;  at  high  temperatures,  the  side-chain,  e.g.  : 

1  Compare  page  165. 


AROMATIC  SERIES 


275 


C6H5  .  CH3  +  Br2  =  C6H4<^         +  HBr 

Ordinary  temperature  Bromtoluene 

C6H5  .  CH3  +  Br2  =  C6H5  .  CH2  .  Br  +  HBr. 

Boiling  temperature  Benzylbromide 

The  aromatic  bromides  which  contain  bromine  in  the  benzene 
nucleus  are  either  colourless  liquids  or  crystals,  which  in  contrast  with 
the  side-chain  substituted  isomers  in  part  possess  an  aromatic  odour, 
and  their  vapours  do  not  attack  the  eyes  and  nostrils.  The  bromine 
is  held  very  firmly  in  them,  more  firmly  than  in  the  aliphatic  bromides, 
and  cannot  be  detected  by  silver  nitrate.  While  the  aliphatic  bromides, 
as  mentioned  under  bromethyl,  decompose  with  ammonia,  alcoholates, 
alkalies,  etc.,  to  form  amines,  ethers,  alcohols,  i 

etc.,  respectively,  these  reagents  do  not  act  on 
the  aromatic  bromides.    The  bromides  contain-    f 
ing.  the  bromine  in  the  side-chain,  behave  like 
their  aliphatic  analogues. 

By  the  action  of  sodium  amalgam,  the  bro- 
mine may  be  replaced  by  hydrogen,  e.g.  : 


C6HB  .  Br  +  H2  =  CGH(! 

From  the 
amalgam 


HBr 


The  aromatic  bromides  are  of  synthetical 
importance,1  especially  for  the  building  up  of 
homologous  hydrocarbons  and  the  preparation 
of  carbonic  acids : 

C6H5.  Br  +  BrC2H5  +  Na2  =  C6H5.C2H5  +  2NaBr 
CfiH3.Br  +  Na2  +  CO2=C6H5.CO.ONa+NaBr 

The  next  preparation  will  take  up  the  first  of 
these  reactions  in  detail. 

The  hydrocarbons  and  most  of  their  deriva- 
tives, like  nitro-,  amido-compounds,  aldehydes, 
acids,  etc.,  may  be  brominated  with  greater  or 
less  ease.  At  this  place,  the  various  modifica- 
tions by  which  the  bromination  may  be  effected 
will  be  mentioned.  If  a  substance  is  very  easily 

brominated.  the  bromine  may  be  used  in  a  diluted  condition.     For  this 
purpose,  either  bromine  water  or  a  mixture  of  bromine   with  carbon 


1  Compare  also  the  Grignard  reaction  (p.  348). 


2/6  SPECIAL   PART 

disulphide  or  glacial  acetic  acid  may  be  employed.  In  many  cases  a 
bromination  may  be  very  well  effected  by  using  gaseous  bromine.  The 
method  of  procedure  is  as  follows :  The  substance  is  spread  out  in  thin 
layers  on  a  watch-glass  and  placed  under  a  glass  bell-jar,  under  which 
is  also  a  small  dish  containing  bromine.  If  it  is  desired  to  cause  bromine 
to  act  gradually,  it  is  allowed  to  drop  from,  a  separating  funnel,  in  con- 
cenf-ated  form  or  in  solution,  on  the  compound  to  be  brominated.  If 
an  extremely  slow  and  very  careful  bromination  is  desired,  the  bromine 
may  be  allowed  to  flow  drop  by  drop  from  a  siphon-shaped  capillary 
tube.  If  bromination  takes  places  with  difficulty,  the  brominating 
mixture  is  heated,  either  in  an  open  vessel  or  in  a  sealed  tube.  In  the 
first  case  the  condensing  apparatus  cannot,  as  usual,  be  connected  to 
the  flask  with  a  cork  or  rubber  stopper,  since  this  is  soon  attacked  and 
destroyed  by  the  bromine.  Instead,  the  condenser  is  well  wrapped 
with  asbestos  twine  and  then  pushed  into  the  conical  part  of  the  neck 
of  the  flask,  the  asbestos  being  pressed  in  with  a  knife.  A  condenser 
of  the  kind  represented  in  Fig.  71  can  also  be  used.  A  long  tube  <r, 
sealed  at  one  end,  is  closed  by  a  two-hole  cork,  through  one  of  which 
passes  a  long  glass  tube  reaching  almost  to  the  bottom  a ;  the  other 
bears  a  short  tube  just  passing  through  the  cork.  Water  is  caused  to 
flow  through  a  ;  it  flows  out  of  b.  This  cooling  apparatus  is  suspended 
in  the  heating-flask,  which  is  selected  with  as  long  a  neck  as  possible. 


18.    REACTION:   FITTIG'S  SYNTHESIS  OP  A  HYDROCARBON 
EXAMPLE  :   Ethyl  Benzene  from  Brombenzene  and  Bromethyl l 

In  a  dry,  round,  i-litre  flask,  provided  with  a  long  reflux  con- 
denser (the  flask  is  supported  on  a  straw  ring  in  an  empty  water- 
bath),  place  27  grammes  of  sodium,  cut  in  scales  as  thin  as 
possible  with  a  sodium  knife,  and  add  100  c.c.  of  alcohol-free, 
dry  ether  prepared  as  described  below.  As  soon  as  this  has 
been  completely  dried  by  the  sodium,  which  may  be  recognised 
by  the  fact  that  the  upper  surface  is  no  longer  disturbed  by  wave- 
like  motions  (after  several  hours'  standing),  pour  through  the  con- 
denser a  mixture  of  60  grammes  of  brombenzene  and  60  grammes 
of  bromethane,  and  allow  to  stand  until  the  next  day.  Should  the 

i  A.  131,303. 


AROMATIC   SERIES  2/7 

liquid  begin  to  boil  gently,  which  may  easily  happen  at  a  summer 
temperature,  cold  water  is  poured  into  the  water-bath.  Water  is 
not  allowed  to  run  through  the  condenser  over  night.  During  the 
reaction,  the  bright  sodium  will  be  changed  to  a  blue  powder,  and 
an  ethereal  solution  of  ethylbenzene  is  formed.  The  ether  is  then 
distilled  off  on  a  water-bath,  and  the  condenser  is  replaced  with 
an  air  condenser  40-50  cm.  long  and  i  cm.  wide,  containing  a 
short  bend.  After  the  flask  has  been  placed  in  an  oblique  posi- 
tion, the  extreme  end  of  its  neck  is  clamped  loosely,  and  the 
ethylbenzene  is  distilled  from  the  sodium  bromide  and  sodium 
by  a  large,  luminous  flame,  which  is  kept  in  constant  motion. 
With  the  use  of  a  Linnemann  apparatus,  the  crude  product  is 
finally  subjected  to  two  distillations.  The  boiling-point  of  pure 
ethylbenzene  is  135°.  Yield,  about  25  grammes. 

The  residue  of  sodium  bromide  and  sodium  remaining  in  the 
flask  must  be  handled  with  extreme  caution.  Water  must  not  be 
added  to  it,  nor  must  it  be  thrown  into  the  sink  or  waste-jars,  nor 
allowed  to  stand  a  long  time  ;  it  is  better  to  throw  the  flask,  which 
cannot  be  used  again,  and  its  contents  into  some  open  place.  The 
sodium  residue  may  be  rendered  harmless  by  throwing  water  on  it 
from  a  great  distance. 

Preparation  of  Anhydrous,  Alcohol-free  Ether 

Shake  200  grammes  of  commercial  ether  in  a  separating  fun- 
nel with  half  its  volume  of  water ;  the  latter  is  allowed  to  run  off, 
and  the  operation  repeated  a  second  time  with  a  fresh  quantity 
of  water,  by  which  the  alcohol  is  removed.  The  ether  is  dried  by 
standing  over  calcium  chloride,  not  too  little,  two  hours.  It  is 
then  filtered  through  a  folded  filter,  and  can  now  be  used  for  the 
above  reaction. 

Fittig's  synthesis  of  the  aromatic  hydrocarbons  is  the  analogue  of 
Wurtz1  synthesis  of  the  aliphatic  hydrocarbons,  e.g.: 

2  C2H5I  +  2  Na  =  C2H5.  C2H5  +  2  Nal 

Ethyl  iodide  Butane 

C6H5.  Br  +  C2H5Br  +  2  Na  =  C6H5.  C2Ha  +  2  NaBr. 

Ethylbenzene 


278  SPECIAL   PART 

The  bromides  of  the  homologues  of  benzene  react  in  a  similar  way,  e.g.  \ 

/CH3  /CH3 

C6H/          +  ICH3  +  Na2  =  C6H4<  +  NaBr  +  Nal. 

\Br  \CH3 

Bromtoluene  Xylene 

The  three  isomeric  bromtoluenes  do  not  react  with  the  same  ease. 
While  the  p-bromtoluene  gives  a  good  yield  of  p-xylene,  the  o:com- 
pound  does  not  give  good  results,  and  the  m-compound  generally  forms 
no  xylene.  Two  alkyl  residues  can  also,  in  many  cases,  be  introduced 
into  a  hydrocarbon  simultaneously,  e.g. : 

/Br  /CH3 

p-C6H4<        +  2 ICH3  +  2  Na2  =  p-C6H4<;          +  2  NaBr  +  2  Nal. 
NBr  \CH3 

The  great  number  of  hydrocarbons  which  may  be  prepared  by  Fittig's 
reaction  is  apparent  from  the  above  examples.  The  value  of  the  reac- 
tion is  still  further  increased  by  the  fact  that  a  halogen  atom  in  the 
side-chain  of  an  aromatic  hydrocarbon  also  reacts  in  the  same  way. 
Though  the  halogen  cannot  be  replaced  by  a  methyl  or  ethyl  radical, 
yet  the  reaction  for  the  introduction  of  the  higher  alkyl  residues  is 
of  great  service,  e.g. : 

C6H5 .  CH2C1  +  CH3 .  CH2 .  CH2Br  +  Na2 

Benzyl  chloride  Propyl  bromide 

=  C6H5.CH2.CH2.CH2.CH3  +  Nad  +  NaBr. 

Butylbenzene 

Also  by  means  of  this  reaction,  two  aromatic  residues  may  be  made 
to  combine,  and  thus  form  the  hydrocarbons  of  the  diphenyl  series,  e.g. : 

2  C6H5.  Br  +  Na2  =  C6H5.  C6H5  +  2  NaBr. 

Diphenyl 

Finally,  the  hydrocarbons  of  the  dibenzyl  series  can  also  be  prepared, 
e.g.  : 

2C6H5.CH2C1  +  Na2  =  C6H5.CH2.CH2.C6H5  +  2NaCl. 

Dibenzyl 

In  conducting  operations  involving  the  Fittig  reaction,  various 
modifications  may  be  introduced,  according  to  the  ease  with  which  the 
reaction  takes  place.  If  the  reaction  occurs  at  the  ordinary  temperature 
easily,  then  an  indifferent  diluent  like  ether,  ligroin,  carbon  disulphide, 


280  SPECIAL   PART 

or  benzene  is  employed.  These  substances  are  not  alike  in  their  activity, 
since  ligro'in  and  benzene  generally  prolong  the  reaction,  and  on  this 
account  find  application  in  a  very  energetic  reaction ;  ether  does  not 
retard  the  reaction,  but  causes  it  to  be  more  regular.  At  times,  the 
reaction-mixture  will  not  act,  even  on  long  standing.  In  this  case, 
the  reaction  can  frequently  be  started  by  a  short  heating,  or  the  addi- 
tion of  a  few  drops  of  ethyl  acetate.  Since  the  use  of  this  compound, 
at  times,  causes  a  very  stormy  action,  it  is  more  advantageous  to  wait 
for  the  reaction  to  begin  spontaneously,  even  if  a  long  time  is  necessary. 
In  syntheses  which  are  moderately  difficult,  the  reaction-mixture,  treated 
with  a  diluent,  can  be  heated  on  the  water-bath  or  in  an  oil-bath; 
while,  if  the  reaction  takes  place  with  great  difficulty,  the  mixture, 
generally  without  dilution,  must  be  heated  in  an  oil-bath.  In  the 
latter  case,  the  reaction  may  be  still  further  facilitated  by  heating  under 
pressure  of  a  mercury  column.  By  this  means,  it  is  possible  to  heat 
the  reacting  substances  in  an  open  vessel  above  their  boiling-points. 
(Fig.  72.) 

19.  REACTION:  SULPHONATION  OF  AN  AROMATIC  HYDRO- 
CARBON (I) 

EXAMPLE  :    (a)    Benzenemonosulphonic  Acid  from   Benzene   and 

Sulphuric  Acid1 

(£)    Sulphobenzide.      Benzenesulphonchloride.      Ben- 
zenesulphonamide 

(a)  To  150  grammes  of  liquid  fuming  sulphuric  acid,  containing 
from  5-8%  of  anhydride,  placed  in  a  200  c.c.  flask  provided 
with  an  air  condenser,  gradually  add,  with  good  shaking  and  cool- 
ing with  water,  40  grammes  of  benzene ;  before  the  addition  of  a 
new  portion,  always  wait  until  the  last  portion,  which  at  first  floats 
on  the  surface  of  the  acid,  dissolves  on  shaking.  The  sulphona- 
tion  requires  about  10-15  niinutes.  The  reaction-mixture  is  then 
added,  with  stirring,  drop  by  drop,  from  a  separating  funnel,  to 
three  to  four  times  its  volume  of  a  cold,  saturated  solution  of 
sodium  chloride  contained  in  a  beaker.  In  order  that  the  solution 
may  not  be  heated  above  the  room  temperature,  the  beaker  is 
!P.  31,  283  and  631;  A.  140,  284;  B.  24,  2121. 


AROMATIC  SERIES  28 1 

placed  in  a  large  water-bath  filled  with  ice-water.  After  some 
time,  but  with  especial  ease  when  the  walls  of  the  vessel  are  rubbed 
with  a  sharp-edged  glass  rod,  the  sodium  salt  of  benzenesulphonic 
acid  separates  out  in  the  form  of  leaflets  of  a  fatty  lustre  ;  the 
quantity  is  increased,  on  long  standing,  to  such  an  extent  that  the 
contents  of  the  beaker  are  converted  into  a  thick  pasty  mass  of 
crystals.  If  the  separation  of  crystals  does  not  begin,  10  c.c.  of  the 
liquid  is  shaken  in  a  corked  test-tube,  and  cooled  by  immersion  in 
water.  The  solidified  content  of  the  tube  is  then  added  to  the  main 
quantity  in  the  beaker.  In  summer,  at  times,  it  may  require  a 
several  hours'  standing  before  the  separation  of  crystals  is  ended. 
The  pasty  mass  of  crystals  is  then  filtered  off  with  suction  on  a 
Biichner  funnel,  firmly  pressed  together  with  a  pestle,  and  washed 
with  a  little  saturated  sodium  chloride  solution. 

To  obtain  the  salt  perfectly  dry  it  is  transferred  to  a  linen  bag 
and  well  squeezed  under  a  screw-press.  After  being  pulverised  it 
is  heated  to  dusty  dryness  in  an  air-bath  at  110°.  Yield,  about 
TOO  grammes. 

If  even  after  long  standing  an  abundant  separation  of  crystals 
does  not  take  place,  the  qause  is  probably  due  to  the  large  per- 
centage of  anhydride  in  the  fuming  sulphuric  acid.  Under  these 
conditions  it  is  diluted  with  concentrated  acid,  and  the  experiment 
repeated.  If  on  the  other  hand  the  acid  is  too  weak,  the  benzene 
will  not  dissolve  in  it.  In  this  case,  during  the  sulphonation  the 
mixture  is  not  cooled,  and  the  reaction  is  allowed  to  take  place  at 
40-50°. 

In  order  to  obtain  pure  sodium  benzenesulphonate,  5  grammes 
of  the  crude  product  is  crystallised  from  absolute  alcohol,  upon 
which  it  is  noticed  that  the  sodium  chloride  mixed  with  it  is  insol- 
uble in  alcohol. 

(b}  In  order  to  obtain  the  by-product,  sulphobenzide,  30 
grammes  of  the  pulverised  salt  is  wanned  with  50  c.c.  of  ether, 
filtered  with  suction  while  hot,  and  washed  with  ether.  After 
evaporating  the  ether,  a  small  amount  of  a  crystalline  residue  is 
obtained ;  this  is  recrystallised  in  a  test-tube  from  ligroi'n.  Melt- 
ing-point, 129°. 


282  SPECIAL   PART 

To  prepare  benzenesulphonchloride  from  sodium  benzenesul 
phonate,  the  extracted  salt  and  unextracted  salt  are  treated  in  a 
dry  flask  (under  the  hood)  with  finely  powdered  phosphorus  pen- 
tachloride  (for  3  parts  dry  sodium  benzenesulphonate,  use  4  parts 
phosphorus  pentachloride).  Mix  by  thorough  shaking.  The 
mixture  is  warmed  £  to  ^  hour  on  an  actively  boiling  water-bath. 
The  cold  reaction-product  is  then  poured  gradually  into  ice-water 
in  a  flask  (use  ten  times  the  weight  of  the  sodium  salt)  ;  it  is  shaken 
up  from  time  to  time,  and,  after  standing  for  two  to  three  hours, 
the  sulphonchloride  is  taken  up  with  ether  and  the  generally  turbid 
ethereal  solution  filtered  ;  the  ether  is  then  evaporated  off.  Yield, 
40-50  grammes. 

In  a  porcelain  dish  10  grammes  of  finely  powdered  ammonium 
carbonate  are  treated  with  about  i  c.c.  of  benzenesulphonchloride, 
and  rubbed  together  intimately ;  the  mixture  is  heated,  with  good 
stirring,  over  a  small  flame,  until  the  odour  of  the  sulphonchloride 
has  vanished.  After  cooling,  it  is  treated  with  water,  filtered  with 
suction,  washed  several  times  with  water,  and  the  benzenesulphon- 
amide  crystallised  from  alcohol  to  which  hot  water  is  added  until 
turbidity  begins.  Melting-point,  156°. 

Under  the  sulphonation  of  aniline  it  was  mentioned  that  the  aromatic 
compounds  differ  from  the  aliphatic  compounds  in  that  they  can  be 
sulphonated  by  the  action  of  sulphuric  acid  ;  i.e.  the  benzene-hydrogen 
atoms  are  replaced  by  the  sulphonic  acid  group,  SO3H.  Thus  the  above 
reaction  takes  place  in  accordance  with  the  following  equation  : 

C6H6  +.  S02/(       -  C6H5 .  S03H  +  H20 
\OH 

Since,  in  the  sulphonation,  an  excess  of  sulphuric  acid  is  always  used, 
after  the  reaction  is  complete  it  is  necessary  to  separate  the  sulphonic 
acid  from  the  excess  of  sulphuric  acid.  Many  sulphonic  acids,  espe- 
cially those  of  the  hydrocarbons,  are  very  easily  soluble  in  water,  so 
that  the  pure  acid  cannot  be  separated  out  on  mere  dilution  with  water, 
as  is  the  case  with  sulphanilic  acid.  There  are  three  methods  in  com- 
mon use  for  the  isolation  of  sulphonic  acids  soluble  in  water.  The 
sulphonic  acids  obtained  most  easily  are  those  difficultly  soluble  in  cold 
sulphuric  acid.  In  this  case  it  is  only  necessary  to  cool  the  sulphon- 


AROMATIC   SERIES  283 

ating  mixture,  and  filter  off  the  sulphonic  acid  separating  out,  with 
suction  over  asbestos  or  glass-wool.  A  second  method  consists  in 
allowing  the  sulphuric  acid  solution  to  flow  into  a  saturated  solution 
of  common  salt ;  in  many  cases  the  difficultly  soluble  (in  sodium  chlo- 
ride solution)  sodium  salt  of  the  sulphonic  acid  separates  out.  Fre- 
quently it  is  more  advantageous  to  use  sodium  acetate,  potassium 
chloride,  ammonium  chloride,  or  other  salts,  instead  of  sodium  chloride. 
Almost  all  soluble  sulphonic  acids,  in  the  form  of  their  alkali  salts,  can 
be  separated  by  these  two  methods  in  the  shortest  time.  In  dealing 
with  a  new  substance,  preliminary  experiments  with  small  quantities 
of  the  substance  are  made  to  determine  which  salt  is  best  adapted  for 
the  separation.  The  Theory  of  Salting  out  is  discussed  at  the  end  of 
this  chapter.  The  third  method,  which  is  the  one  generally  appli- 
cable, depends  upon  the  property  of  sulphonic  acids,  of  forming  soluble 
salts  of  calcium,  barium,  and  lead  in  contradistinction  to  sulphuric  acid. 
If  the  sulphuric  acid  solution,  diluted  with  water,  is  neutralised  with  the 
carbonate  of  one  of  these  metals  and  then  filtered,  the  filtrate  contains 
only  the  corresponding  salt  of  the  sulphonic  acid,  while  the  sulphuric 
acid  in  the  form  of  calcium,  barium,  or  lead  sulphate  remains  on  the 
filter.  If  the  alkali  salts  of  the  sulphonic  acids  are  desired,  the  water 
solution  of  one  of  the  above  salts  is  treated  with  the  alkali  carbonate 
until  a  precipitate  is  no  longer  formed.  The  precipitate  is  filtered  off, 
and  the  pure  alkali  salt  of  the  sulphonic  acid  is  obtained  in  solution, 
which,  on  evaporation  to  dryness,  yields  the  salt  in  the  solid  condition. 

In  order  to  obtain  the  free  sulphonic  acid,  the  lead  salt  is  prepared 
and  then  decomposed  with  sulphuretted  hydrogen. 

The  sulphonic  acids  of  the  hydrocarbons  are  generally  colourless, 
crystallisable  compounds,  very  easily  soluble  in  water,  insoluble  in  ether, 
behaving  like  strong  acids.  By  heating  with  hydrochloric  acid,  under 
pressure  if  necessary,  or  by  the  action  of  steam,  the  sulphonic  acid  group 
may  be  split  off,  e.g.  : 

C6H5 .  S03H  +  H20  =  C6H6  +  H2S04 

This  reaction  is  of  importance  in  many  cases  for  the  separation  of 
hydrocarbon  mixtures.  If  under  certain  conditions  one  hydrocarbon 
is  sulphonated,  and  another  is  not,  the  latter  can  be  separated  from  the 
former  by  removing  the  sulphuric  acid  solution  of  the  sulphonic  acid 
of  the  first,  and  from  this  the  original  hydrocarbon  may  be  regenerated 
by  one  of  the  methods  mentioned. 

Of  particular  importance  is  the  behaviour  of  sulphonic  acids  when 


284  SPECIAL  PART 

fused  with  caustic  potash  or  caustic  soda,  by  which  the  sulphonic  acid 
group  is  eliminated  and  a  phenol  formed : 

C6H3 .  SO3K  +  KOH  =  C6H5.  OH  +  K2SO3 

With  benzenesulphonic  acid  this  important  reaction  does  not  take 
place  smoothly;  for  this  reason  the  directions  for  carrying  it  out  prac- 
tically will  be  given  later  in  another  place  (see  /3-naphthol).  Poly- 
acid  phenols  may  also  be  obtained  from  poly-basic  sulphonic  acids. 
The  formation  of  m-dioxybenzene  or  resorcinol  from  benzenedisul- 
phonic  acid  is  of  practical  value  : 

,OH 

C6H4(SO,K)2  +  2  KOH  =  CeH  /         +  2  K2SO3 

X)H 

If  an  alkali  salt  of  a  sulphonic  acid  mixed  with  potassium  cyanide  or 
potassium  ferrocyanide  is  subjected  to  dry  distillation,  the  sulphonic 
acid  group  is  replaced  by  cyanogen  and  an  acid-nitrile  is  obtained,  e.g.  : 

C6H5.  SO3K  +  KCN  =  C6H5.CN  +  K2SO3 

Benzonitrile 

The  sulphonic  acids  behave  toward  phosphorus  pentachloride  like  the 
carbonic  acids,  with  the  formation  of  acid-chlorides  : 

C6H5.  SO8Na  +  PC15  =  C6H5.  S02.C1  +  NaCl  +  POC13 

Benzenesulphonchloride 

The  sulphonchlorides  are  not  decomposed,  or  only  slightly  decom 
posed  by  cold  water.  In  order  to  separate  them  from  the  phos- 
phorus oxychloride,  the  mixture  is  generally  poured  into  cold  water; 
after  long  standing  the  oxychloride  is  converted  into  phosphoric  acid, 
and  the  acid-chloride  insoluble  in  water  is  obtained  by  decanting 
the  water  or  extracting  with  ether ;  or  in  case  it  is  solid,  by  filtering. 
The  sulphonchlorides  are  generally  distinguished  by  a  very  characteristic 
odour.  They  can  be  distilled  in  a  vacuum  only,  without  decomposition. 
Treated  with  ammonia  they  form  sulphonamides,  which  crystallise  well 
and  are  used  for  the  characterisation  of  the  sulphonic  acids  : 

C6H5 .  SO2 .  Cl  +  NH3  =  QHS ,  SO2 .  NH2  +  HC1 

Benzenesulphonamide 

In  the  sulphonamides,  in  consequence  of  the  strongly  negative 
character  of  the  X .  SO2-group,  the  hydrogen  of  the  amido-group  is 


AROMATIC   SERIES  285 

so  easily  replaced  by  metals,  that  they  dissolve  in  water  solutions  or 
the  alkalies  to  form  salts  of  the  amide.  (Try  it.)  If  a  sulphon- 
chloride  is  allowed  to  stand  a  long  time  with  an  aliphatic  alcohol,  a 
sulphonic  acid  ester  is  formed,  e.g.  : 

C6H5  .  SO2  .  Cl  -f  C2H5  .  OH  =  C6H,  .  SO2  .  OC2H5  +  HC1 

Benzenesulphonic  ester 

If  this  is  now  .warmed  with  an  alcohol,  an  aliphatic  ether  is  formed, 
with  the  generation  of  the  sulphonic  acid,  e.g.  : 

C6H5  .  S02  .  OC,H5  +  C2H5  ,OH  =  C0H5  .  SO3H  +  C2H5  .  O  .  C2H5 

The  formation  of  ether  in  this  case  is  analogous  to  the  formation  of 
ethyl  ether  on  heating  ethyl  sulphuric  acid  with  alcohol  : 


SO2  +  C2H,  .  OH  =  H,SO4  +  C2H5  .  0  .  C2H 


Since  this  reaction  is  continuous,  and  since  the  benzene  sulphonic  acid 
formed  in  the  reaction  is  a  weaker  acid  than  sulphuric  acid,  and  conse- 
quently does  not  carbonise  the  alcohol  like  sulphuric  acid,  the  operation 
may  be  continued  for  a  long  time  uninterruptedly.  For  these  reasons 
recently  attempts  have  been  made  to  employ  the  aromatic  sulphonic 
acids  for  the  technical  preparation  of  ether.  If  the  sulphonation  is 
effected  as  above  with  fuming  sulphuric  acid,  in  many  cases,  besides 
the  sulphonic  acid  a  small  quantity  of  sulphone  is  formed,  e.g.  : 


2C6H6+S03  =  S02         +  H20 
XCCH5 

Diphenylsulphone 
=  Sulphobenzide 

For  sulphonating  purposes,  either  ordinary  concentrated  sulphuric  acid 
or  the  so-called  monohydrate  or  fuming  sulphuric  acid  of  various  grades 
is  used,  according  to  the  conditions.  The  reaction  is  conducted  with 
cooling,  at  the  room  temperature,  or  with  heating. 

To  facilitate  the  elimination  of  water,  phosphorus  pentoxide  or 
potassium  sulphate  may  be  added  to  the  sulphonating  mixture. 

In  some  cases  it  is  of  advantage  to  use  chlorsulphuric  acid  instead 


286  SPECIAL   PART 

of  sulphuric  acid;  the  reaction  takes  place  in  accordance  with  the  fol. 
lowing  equation  : 

C6H6  +  Cl  .  S03H  =  C6H5  .  S03H  +  HC1 

Theory  of  Salting  out.  —  The  process  of  salting  out  depends 
upon  the  following  conditions  :  According  to  the  theory  of  electro- 
lytic dissociation,  the  water  solution  of  an  electrolyte  like  sodium 
benzenesulphonate,  contains  the  ions  of  C6H5SO3'  —  and  Na*  —  ,  and 
the  electrically  neutral,  undissociated  molecules  of  C6H5.SO3Na. 
Now  it  must  not  be  assumed  that  in  such  a  solution,  at  any  given 
time,  ions  and  molecules  remain  in  this  condition  ;  it  is  more  likely 
that  as  the  ions  of  C6H5.SO3'  —  and  Na*  —  come  into  contact  with 
each  other  under  favourable  conditions,  they  recombine  forming 
new  molecules,  while  at  the  same  time  undissociated  molecules 
dissociate.  We  therefore  have  a  dynamic  equilibrium  of  a  reversi- 
ble reaction  (similar  to  that  mentioned  under  ethyl  acetate),  which 
may  be  expressed  by  the  following  equation  : 

C6H5  .  S(V  +  Na'  ^±  C6H5  .  SO3Na 

If  we  indicate  the  concentrations  of  the  ions  and  molecules  by 
CceHg  .  so3,  CNH  and  Cc6H5  .  so3Na,  the  mass  action  equation  for  this 
equilibrium  will  be  : 

.  soa  X  CNa  _ 


Cc6H5  .  S03Na 
Or,  (II)    Cc6H5  .  S03  X  CNa  =  K  X  Cc6H5  .  SO3Na 

where  K  is  the  dissociation  constant.  Suppose  we  add  solid  com- 
mon salt  to  such  a  solution  and  take  care  that  no  solid  salt  sepa- 
rates out  ;  then  since  common  salt  is  a  strong  electrolyte,  it  will 
largely  dissociate  into  ions  in  the  solution,  and  the  concentration 
of  Na-ions  will  be  increased.  But  since  the  constant  K  has  the 
same  value  for  all  proportions,  the  increase  of  CNa  will  decrease 
Cc6H5  .  so3  and  will  consequently  increase  Cc6H5  .  so3Na-  In  this 
way  only  can  K  have  a  constant  value.  Hence,  the  addition 
of  common  salt  will  cause  a  decrease  in  the  number  of  C6H5  .  SO3- 
ions,  and  an  increase  in  the  number  of  undissociated  molecules. 
This  is  known  as  "  diminution  in  dissociation  by  the  addition  of 
an  electrolyte  containing  one  ion  in  common."  If  we  now  con- 
tinue to  add  more  common  salt,  the  concentration  of  C<jH5  .  SO3- 
ions  will  constantly  diminish,  while  that  of  the  undissociated 
molecules  will  constantly  increase,  and  a  point  will  finally  be 
reached  when  the  solution  will  become  saturated  with  undis- 
sociated molecules  ;  i.e.  a  maximum  number  of  molecules  will  be 
held  in  solution.  If  more  common  salt  is  now  added,  the  newly 
formed  undissociated  molecules  will  separate  out  in  the  solid  form. 


AROMATIC   SERIES  287 

At  this  stage  CcRH5.so.sNa  becomes  a  constant,  and  the  product 
of  the  concentration  of  ions  is  called  the  "solubility  product." 
When  the  solid  begins  to  separate  out,  the  amount  of  the  soluble 
undissociated  portion  becomes  independent  of  the  presence  of  the 
electrolyte  having  a  common  ion,  although  the  concentration  of 
the  ions  is  variable,  and  is  determined  by  the  solubility  product 
Thus,  to  mention  an  extreme  example,  in  one  case  Cc^H^sOg 
may  be  large  and  CNS  small,  while  in  another  case  CNa  may  be 
large  and  CcfiH5.so3  small.  Thus  it  becomes  impossible,  even 
by  the  addition  of  a  large  quantity  of  an  electrolyte  having  a  com- 
mon ion,  to  salt  out  the  undissociated  molecules  that  are  in  solu- 
tion. This  may  be  termed  the  solution-tension  of  the  undissociated 
molecules,  and  corresponds  with  Dalton's  law  of  the  vapour-tension 
of  a  substance,  which  is  independent  of  external  pressure.  The 
vapour-tension  of  liquid  water  whether  it  be  confined  in  a  vacuous 
space,  or  kept  at  a  definite  pressure  in  physical  equilibrium  with 
other  gases,  will  always  be  the  same  at  any  given  temperature. 

In  the  practical  example  described  above,  the  conditions  are 
somewhat  complicated.  Neglecting  the  excess  of  sulphuric  acid 
used,  we  have  a  water  solution  of  benzenesulphonic  acid,  treated 
with  common  salt.  But  according  to  the  ionic  dissociation  theory, 
such  a  solution  will  contain  ions  of  C6H5 .  SO3',  Cl',  Na"  and 
H'  in  addition  to  undissociated  molecules  of  C6H5 .  SO3Na,  NaCl, 
C6H5 .  SO3H  and  HC1. 

But  the  main  fact  to  be  taken  into  consideration  is  the  equi- 
librium existing  between  C6H5 .  SO3',  Na'  and  C6H5 .  SO3Na,  which 
is  not  influenced  by  the  presence  of  other  substances.  When  the 
solubility  limit  for  this  equilibrium  is  exceeded  by  increasing 
the  number  of  Na-ions,  by  the  addition  of  common  salt,  then 
the  undissociated  sodium  benzenesulphonate  will  separate  out 
in  the  solid  state. 

It  is  hardly  necessary  to  state  that  with  certain  solubility  pro- 
portions, not  only  solid  salt,  but  also  its  solution,  can  be  used  for 
salting  out. 

20.  REACTION:   REDUCTION  OF  A  SULPHON CHLORIDE  TO  A 
SULPHINIC  ACID  OR   TO  A  THIOPHENOL 

EXAMPLES:    (a)  Benzenesulphinic  Acid.1     (ft)  Thiophenol2 

(a)  Heat  40  grammes  of  water  to  boiling  in  a  300  c.c.  flask 
provided  with  a  short  reflux  condenser  and  a  dropping  funnel ; 
add  10  grammes  of  zinc  dust,  and  without  further  heating  by  the 
flame,  gradually  allow  to  flow  in  from  the  funnel,  with  thorough 

i  6.9,1585.  2  A.  119, 142 


288  SPECIAL    PART 

shaking,  10  grammes  of  benzenesulphonchloride  in  small  portions. 
After  each  addition  wait  until  the  vigorous  reaction  accompanied 
by  a  hissing  sound  has  moderated.  The  mixture  is  then  heated 
a  few  minutes  over  a  small  flame,  filtered  after  cooling  from  the 
precipitate  of  zinc  dust  and  the  zinc  salt  of  benzenesulphinic  acid, 
and  the  precipitate  washed  several  times  with  water.  The  insig- 
nificant-looking gray  precipitate  is  the  reaction-product,  and  not 
the  filtrate,  which  can  be  thrown  away.  The  precipitate  is  then 
heated  for  about  ten  minutes,  not  quite  to  boiling,  with  a  solution 
of  10  grammes  of  dehydrated  sodium  carbonate  in  50  c.c.  of  water, 
and  then  filtered  with  suction.  The  precipitate  remaining  on  the 
filter  is  worthless,  while  the  filtrate  contains  the  sodium  benzene- 
sulphinate  in  solution.  This  is  evaporated  to  about  one-half  its 
original  volume,  and,  after  cooling,  acidified  with  dilute  sulphuric 
acid,  upon  which  the  free  benzenesulphinic  acid  separates  out  in 
colourless  crystals ;  the  separation  is  facilitated  by  rubbing  the 
sides  of  the  vessel  with  a  glass  rod.  After  filtering,  the  substance 
is  recrystallised  from  a  little  water.  Melting-point,  83-84°. 

Should  the  free  acid  not  separate  on  acidifying  the  sodium  salt, 
it  is  extracted  several  times  with  ether;  this  is  evaporated,  and 
the  residue,  in  case  it  does  not  solidify  of  itself,  is  rubbed  with  a 
glass  rod  and  then  recrystallised. 

(b)  In  order  to  convert  the  residue  of  benzenesulphonchloride 
obtained  in  Reaction  19  into  thiophenol,  it  is  heated  on  a  water- 
bath  with  granulated  tin  and  concentrated  hydrochloric  acid,  in  a 
large  flask  provided  with  a  long  reflux  condenser  and  dropping 
funnel ;  the  sulphonchloride  is  allowed  to  flow  in  gradually  from 
the  dropping  funnel.  (To  i  part  of  the  chloride  use  2\  parts  of 
tin  and  5  parts  of  concentrated  acid.)  The  heating  is  continued 
until  most  of  the  tin  is  dissolved.  The  thiophenol  formed  is  dis- 
tilled over  with  steam,  extracted  with  ether,  dried  over  anhydrous 
Glauber's  salt,  and,  after  the  evaporation  of  the  ether,  rectified. 
Boiling-point,  173°. 

In  the  preparation  of  thiophenol,  care  is  taken  that  there  are 
no  flames  in  the  neighbourhood  of  the  flask  in  which  the  reaction 
is  conducted,  otherwise  there  may  be  an  explosion  of  the  mixture 


AROMATIC   SERIES  289 

of  oxygen  and  hydrogen.  Since  the  thiophenol  possesses  an 
extremely  unpleasant  odour,  and  the  vapours  attack  the  eyes, 
causing  tears,  the  experiment  must  not  be  carried  out  in  the 
laboratory,  but  in  a  side  room  (hydrogen  sulphide  room),  or  in 
the  open  air,  in  the  basement,  or  at  least  under  a  hood  with  a 
good  draught.  Further,  care  must  be  taken  not  to  allow  the 
substance  to  come  in  contact  with  the  skin,  since  it  produces  a 
violent  burning. 

If  zinc  dust  is  allowed  to  act  on  a  sulphonchloride,  the  zinc  salt  of 
the  sulphinic  acid  is  formed : 

C6H5.S02.C1  C6H5.S02\ 

>Zn  +  ZnCL 
C6H5 .  SO2 .  Cl  +  ZnZn  =  C6H5 .  SO2/ 

Zinc  benzenesulphinate 

The  zinc  salts  thus  formed  are  insoluble  in  water,  and  can  be  easily 
obtained  by  filtering  off.  In  order  to  prepare  the  free  sulphinic  acid 
from  a  zinc  salt,  it  is  first  converted  into  the  easily  soluble  sodium  salt 
by  boiling  with  a  sodium  carbonate  solution  ;  the  solution  of  the  sodium 
salt  is  concentrated,  and  the  free  acid  is  precipitated  with  dilute  sulphuric 
acid.  The  sulphinic  acids  differ  from  the  sulphonic  acids  in  that  they 
are  difficultly  soluble  in  cold  water,  and  can,  therefore,  be  recry stall ised 
from  water.  They  are  also  soluble  in  ether,  in  which  sulphonic  acids 
do  not  dissolve.  On  fusing  with  potassium  hydroxide,  the  sulphinic 
acids  pass  over  to  the  hydrocarbons  : 

C6H5.  S02K  +  KOH  =  K2S03  +  C6H6 

If  they  are  reduced,  a  thiophenol  is  finally  obtained,  as  above: 
C6H5 .  SO2H  +  4  H  =  C6H5 .  SH  +  2  H2O 

The  thiophenols  may  also  be  prepared  by  the  direct  reduction  of  the 
sulphonchlorides : 

C6H5 .  S02C1  +  6  H  =  C6H5 .  SH  +  2  H20  +  HC1 

The  thiophenols  are  liquids  of  unpleasant  odours ;  the  higher  mem- 
bers of  the  series  are  solids.     Like  the  mercaptans  of  the  aliphatic 
series,  they  form  difficultly  soluble  salts  with  lead  and  mercury, 
u 


290  SPECIAL   PART 

EXPERIMENT  :  Dissolve  mercuric  chloride  or  lead  acetate  in  a 
test-tube  with  alcohol  by  heating ;  then  cool,  and  filter.  If  the 
alcoholic  solution  is  treated  with  a  few  drops  of  thiophenol,  a 
precipitate  of  the  difficultly  soluble  salt  is  obtained.  The  lead 
salt  is  yellow,  and  possesses  the  composition  represented  by  the 
formula : 

(C6H5.S)2Pb 

In  the  air,  and  on  treatment  with  oxidising  agents  like  nitric  acid, 
chromic  acid,  iodine,  etc.,  the  thiophenols  are  oxidised  to  disulphides : 

2  C6H5 .  SH  +  O  =  C6H5 .  S— S  .  C6H.  +  H2O 

EXPERIMENT  :  A  few  drops  of  phenyl  mercaptan  are  dissolved  in 
alcohol,  treated  with  some  ammonia,  and  evaporated  to  dryness  on 
the  water-bath  in  a  watch-glass.  (Under  the  hood.)  Colourless 
needles  of  the  disulphide  remain.  Melting-point,  61°. 

By  reduction  the  disulphides  are  easily  converted  back  to  the  thio- 
phenols : 

C6H5 .  S— S  .  C6H5  +  2  H  =  2  C6H5 .  SH 

Like  the  phenols  the  thiophenols  have  the  power  of  forming  ethers, 

C6HS.SCH,     =Thioanisol, 
C6H5 .  S  .  C6H5  =  Phenylsulphide. 


21.  REACTION:  SULPHONATION  OP  AN  AROMATIC  HYDRO- 
CARBON (II) 

EXAMPLE  :  p-Naphthalenesulphonic  Acid 

A  mixture  of  50  grammes  of  finely  pulverised  naphthalene  and 
60  grammes  of  pure  concentrated  sulphuric  acid  is  heated  in  an 
open  flask  in  an  oil-bath  for  4  hours  to  170-180°.  After  cool- 
ing, the  solution  is  carefully  poured,  with  stirring,  into  i  litre  of 
water,  and  the  naphthalene  not  attacked  is  filtered  off;  in  case 
the  filtration  takes  place  very  slowly,  only  the  turbid  liquid  is 
poured  off  from  the  coarse  pieces  of  naphthalene ;  the  mixture  is 


AROMATIC  SERIES  2QI 

neutralised  at  the  boiling  temperature  in  a  large  dish  with  a  paste 
of  lime,  not  too  thin,  prepared  by  triturating  about  70  grammes 
of  dry  slaked  lime  with  water.  The  mixture  is  filtered  as  hot 
as  possible  through  a  filter-cloth,  which  has  been  previously 
thoroughly  moistened  (see  page  61)  and  the  precipitate  washed 
with  hot  water.  The  filter-cloth  is  then  folded  together  and 
thoroughly  squeezed  out  in  another  dish  ;  the  expressed,  generally, 
turbid  liquid,  after  filtering,  is  united  with  the  main  quantity. 
The  solution  is  then  evaporated  in  a  dish  over  a  free  flame  until 
a  test-portion  will  solidify  to  a  crystalline  paste  on  rubbing  with  a 
glass  rod.  After  the  solution  has  been  allowed  to  stand  over  night 
the  calcium  /3-naphthalenesulphonate  is  filtered  off  with  suction, 
washed  once  with  a  little  water,  pressed  firmly  together  with  a 
pestle,  and  spread  out  on  a  porous  plate.  In  order  to  obtain  the 
sodium  salt,  it  is  dissolved  in  hot  water,  and  the  solution  gradually 
treated  with  a  concentrated  solution  of  50  grammes  of  crystallised 
sodium  carbonate  until  a  test-portion  filtered  off  no  longer  gives 
a  precipitate  with  sodium  carbonate.  After  cooling,  the  precipi- 
tate of  calcium  carbonate  is  filtered  off  with  suction,  washed  with 
water,  and  the  filtrate  evaporated  over  a  free  flame  until  crystals 
begin  to  separate  from  the  hot  solution.  After  standing  several 
hours  at  the  ordinary  temperature,  the  crystals  are  filtered  off,  and 
the  mother-liquor  further  concentrated  ;  after  long  standing,  the 
second  crystallisation  is  filtered  off,  and  the  mixture  of  the  two 
lots  of  crystals  dried  on  the  water-bath.  Yield,  60-70  grammes. 

Naphthalene  is  sulphonated  on  heating  with  sulphuric  acid,  in  ac- 
cordance with  the  following  equation  : 


There  is  formed  not  as  in  the  case  of  benzene,  in  which  the  six 
hydrogen  atoms  are  equivalent,  a  single  sulphonic  acid,  but  a  mixture 
of  two  isomeric  sulphonic  acids  : 


SO3H 


jo03H. 


o-Naphthalenesulphonic  acid        /3-Naphthalenesulphonic  acid 


SPECIAL  PART 

According  to  the  temperature  at  which  the  sulphonation  takes  place, 
more  of  one  than  of  the  other  acid  is  formed  ;  at  lower  temperatures  an 
excess  of  the  a-acid  is  obtained,  at  higher  an  excess  of  the  /2-acid.  If 
the  mixture  is  heated  to  100°,  a  mixture  of  4  parts  of  the  a-acid  and 
i  part  of  the  y3-acid  is  formed,  while  at  170°  a  mixture  of  3  parts  of 
the  /3-acid  and  I  part  of  the  a-acid  is  obtained.  In  order  to  separate 
the  sulphonic  acids  from  the  excess  of  sulphuric  acid,  advantage  is 
taken  of  the  fact  that  sulphonic  acids  differ  from  sulphuric  acid  in  that 
they  form  soluble  salts  of  calcium,  barium,  and  lead,  as  mentioned 
under  benzenesulphonic  acid.  For  the  separation  of  the  sulphonic  acid 
from  sulphuric  acid,  the  calcium  salt  is  prepared  by  neutralising  the 
acid  mixture  with  chalk  or  lime,  since  it  is  cheaper  than  lead  carbonate 
or  barium  carbonate.  This  method  is  followed  technically  on  the  large 
scale  as  well  as  in  laboratory  preparations.  Since  the  calcium  salts  of 
the  two  isomeric  sulphonic  acids  possess  a  very  different  solubility  in 
water,  —  at  10°  i  part  of  the  a-salt  dissolves  in  16.5  parts  of  water,  and 
i  part  of  the  /3-salt  dissolves  in  76  parts  of  water,  —  the  /3-salt,  which  is 
more  difficultly  soluble,  and  consequently  crystallises  out  first,  can  be 
separated  by  fractional  crystallisation  from  the  a-salt  which  remains  in 
solution.  For  the  conversion  into  naphthol  the  calcium  salt  cannot  be 
used  directly ;  it  must  first  be  changed  into  the  sodium  salt  by  treatment 
with  sodium  carbonate : 

(C10H7 .  S03)2Ca  +  Na2C03  =  2  C10Hr .  SO3Na  +  CaCO3 . 

In  order  to  remove  the  last  portions  of  the  a-salt,  it  is  advisable  not 
to  evaporate  the  solution  of  sodium  salt  directly  to  dryness,  but  to 
allow  the  more  difficultly  soluble  /3-salt  to  crystallise  out,  upon  which 
the  a-salt  remains  dissolved  in  the  mother-liquor. 

The  reactions  of  the  naphthalenesulphonic  acids  are  similar  to  those 
given  above  under  benzenesulphonic  acid.  It  is  still  to  be  mentioned 
that  the  a-acid  is  converted  into  the  /3-acid  by  heating  with  concen- 
trated sulphuric  acid  to  almost  200° ;  a  reaction  which  is  explained  by 
the  fact  that  the  sulphonic  acid  decomposes  in  the  small  amount  of  water 
always  present,  'into  naphthalene  and  sulphuric  acid,  and  that  the 
former  is  then  sulphonated  to  the  /3-acid  at  the  higher  temperature 
(200°) .  The  sulphonation  of  naphthalene  to  the  a-  and  /3-acids  is 
carried  out  on  the  large  scale  in  technical  operations,  since  when  fused 
with  sodium  hydroxide  these  acids  yield  naphthols  of  great  importance 
for  the  manufacture  of  dyes.  The  next  preparation  deals  with  this 
reaction. 


AROMATIC   SERIES 


22.    REACTION:    CONVERSION    OP    A    SULPHONIC    ACID   INTO    A 

PHENOL 

EXAMPLE  :  p-Naphthol  from  Sodium-p-Naphthalene  Sulphonate  and 
Sodium  Hydroxide1 

In  order  to  convert  sodiums-naphthalene  sulphonate  into 
/3-naphthol  the  proportions  of  the  necessary  reagents  used  are  : 

10  parts  sodium-/?-naphthalene  sulphonate  ; 
30  parts  sodium  hydroxide,  as  pure  as  possible ; 
i  part  water. 

The  sodium  hydroxide  is  broken  in  pieces  about  a  centimetre  in 
length,  or  the  size  of  a  bean,  treated  with  the  water,  and  heated 
in  a  nickel  crucible  (a  crucible  n  cm.  high  and  8  cm.  in  diameter 
is  a  convenient  size),  with  stirring,  to  280°  (Fig.  73).  The  stirring 
is  done  with  a  thermometer,  the  lower  end  of  which  is  protected 
by  a  case  of  copper  or  nickel,  about  16  cm.  long  and  8  mm.  wide. 
This  is  supported  by  a  cork,  containing  a  narrow  canal  at  the 
side,  fitting  the  case.  In  order  to  be  able  to  determine  the  tem- 
perature as  exactly  as  possible,  a  layer  of  oil  i  cm.  high  is  placed 
in  the  case,  in  which  the  bulb  of  the  thermometer  is  immersed. 
If  the  stirring  is  done  with  the  case,  the  upper  portion  is  covered 
with  several  layers  of  asbestos  board,  secured  with  wire,  or  a  cork 
is  pushed  over  the  case  (Fig.  73).  Since,  on  fusion  of  the  sodium 
hydroxide,  a  troublesome  spattering  takes  place,  the  hand  is 
protected  by  a  glove,  and  the  eyes  by  glasses.  As  soon  as  the 
temperature  reaches  280°,  the  heating  is  continued  with  a  some- 
what smaller  flame,  and  the  sodium  naphthalene  sulphonate  is 
gradually  added,  with  stirring.  After  each  new  addition,  the  tem- 
perature falls  somewhat ;  no  more  of  the  salt  is  added,  until  the 
temperature  again  reaches  280°.  After  all  the  salt  is  added,  the 
flame  is  made  somewhat  larger,  upon  which  the  fusion  becomes 
viscid  with  evolution  of  steam  and  frothing,  until  finally,  at  about 
310°,  the  real  reaction  takes  place.  After  the  temperature  is  held 


1  E.  Fischer,  Prep,  of  Organic  Compounds,  7  Ed.  page  55.    Z.  1867,  299. 


294  SPECIAL   PART 

at  310-320°  for  about  5  minutes,  the  fusion  becomes  liquid, 
and  the  reaction  is  complete.  The  melted  mass  is  then  poured 
in  a  thin  layer  on  a  strong  copper  plate  the  edges  of  which 
have  been  turned  up.  The  portions  of 
dark  sodium  naphtholate  may  be  easily 
distinguished  from  the  brighter  caustic 
soda.  After  cooling,  the  solid  mass  is 
broken  up  and  dissolved  in  water.  The 
naphthol  is  precipitated  at  the  boiling 
temperature  with  concentrated  hydro- 
chloric acid  (under  the  hood),  and  after 
cooling  is  extracted  with  ether.  The 
ethereal  solution  is  dried  over  anhydrous 
Glauber's  salt,  and  then  the  ether  is 
evaporated  in  an  apparatus  similar  to 
the  one  described  on  page  35  ;  a  frac- 
tionating flask  with  a  very  wide  condens- 
ing tube  is  used.  After  the  removal  of 
the  ether,  the  naphthol  remaining  back  is 
distilled  over  without  the  use  of  a  con- 
denser. Melting-point,  123°.  Boiling-point,  286°.  Yield,  half 
the  weight  of  the  sulphonate  used. 

As  above  indicated,  in  a  sodium  hydroxide,  or  potassium  hydroxide 
fusion  of  a  sulphonic  acid,  besides  the  phenol,  the  alkali  sulphite  is 
formed,  e.g.  : 

C10H7 .  S03Na  -f  2  NaOH  =  C10H7 .  ONa  +  Na2SO3  +  H2O 

Sodium  naphtholate 

The  free  phenol  is,  therefore,  not  directly  obtained  on  fusion,  but 
the  alkali  salt  of  it,  from  which,  after  the  solution  of  the  fusion  in  water, 
the  phenol  is  liberated  on  acidifying  with  hydrochloric  acid. 

The  reaction  just  effected  is  in  practice  carried  out  on  the  largest 
scale  in  iron  kettles  to  which  stirring  apparatus  is  attached.  /?-naph- 
thol  as  well  as  its  numerous  mono-  and  poly-sulphonic  acid  derivatives 
obtained  by  treatment  with  sulphuric  acid  find  extensive  application  for 


AROMATIC  SERIES  2Q5 

the  manufacture  of  azo  dyes.  Further,  from  the  y8-naphthol,  /3-naph- 
thylamine  is  prepared  by  the  action  of  ammonia  under  pressure : 

C10H7.OH  +  NH,  =  C10H7.NH2  +  H2O, 

which  also  finds  technical  use  for  the  manufacture  of  azo  dyes,  as  such 
and  in  the  form  of  its  sulphonic  acids.  a-Naphthol  is  also  prepared  in 
the  same  way  by  fusion  of  a-sodiumnaphthalene  sulphonate  with  sodium 
hydroxide,  although  not  in  so  large  quantities  as  the  /2-naphthol. 

The  phenols,  in  consequence  of  the  negative  character  of  the  aromatic 
hydrocarbon  residue,  are  weak  acids  which  dissolve  in  water  solutions 
of  the  alkalies  to  form  salts.  Still  the  acid  nature  is  so  weak  that  the 
salts  can  be  decomposed  by  carbon  dioxide ;  use  is  frequently  made  of 
this  property  for  the  purification  and  separation  of  phenols. 

EXPERIMENT:  A  mixture  of  /8-naphthol  and  benzo'ic  acid  is 
dissolved  in  a  diluted  caustic  soda  solution,  and  carbon  dioxide 
passed  into  it  for  a  long  time.  /?-Naphthol  only  separates  out ; 
this  is  filtered  off.  The  filtrate  is  acidified  with  concentrated 
hydrochloric  acid  upon  which  the  benzo'ic  acid  is  precipitated. 

The  naphthols  differ  from  the  phenols  of  the  benzene  series,  in  that 
their  hydroxyl  groups  are  more  capable  of  reaction  than  those  of  the 
phenols,  cresols,  etc.  While,  for  example,  the  ether  of  phenol  cannot 
be  prepared  from  the  phenol  and  corresponding  alcohol  by  abstracting 
water : 

(C6H-.OH  +  CH3.OH  =  C6H5.O.CH3  +  H2O), 

Does  not  take  place 

but  can  only  be  obtained  by  the  action  of  halogen  alkyls,  or  salts  of 
alkyl  sulphuric  acid  on  phenol  salts  : 

C6H8.  ONa  +  ICH3  =  C8HB.  O .  CH,  +  Nal. 

By  heating  the  naphthols  with  an  aliphatic  alcohol  and  sulphuric  acid 
the  ethers  are  easily  prepared : 

C10H7.OH  +  CH3.OH  =  C10H7.O.CH34  H2O. 

NaphthylmethyJ  ether 


296  SPECIAL  PART 

23.   REACTION:    NITRATION  OP  A  PHENOL 
EXAMPLE  :   o-  and  p-Nitrophenol 

Dissolve  80  grammes  of  sodium  nitrate  in  200  grammes  of 
water  by  heating;  after  cooling,  the  solution  is  treated,  with 
stirring,  with  100  grammes  of  concentrated  sulphuric  acid.  To 
the  mixture  cooled  to  25°  contained  in  a  beaker,  add  drop  by 
drop,  from  a  separating  funnel,  with  frequent  stirring,  a  mixture 
of  50  grammes  of  crystallised  phenol  and  5  grammes  of  alcohol, 
melted  by  warming.  During  this  addition  the  temperature  is  kept 
between  25-30°  by  immersing  the  beaker  in  water.  Should  the 
phenol  solidify  in  the  separating  funnel,  it  is  again  melted  by  a 
short  warming  in  a  large  flame.  After  the  reaction-mixture  has 
been  allowed  to  stand  for  two  hours  with  frequent  stirring,  it  is 
treated  with  double  its  volume  of  water ;  the  reaction-product 
collects  as  a  dark  oil  at  the  bottom  of  the  vessel.  The  principal 
portion  of  the  water  solution  is  then  decanted  from  the  oil,  this  is 
washed  again  with  water,  and  after  the  addition  of  %  litre  of  water, 
is  distilled  with  steam  until  no  more  o-nitrophenol  passes  over. 
Concerning  the  removal  of  the  o-nitrophenol  solidifying  in  the 
condenser,  see  page  39  (temporary  removal  of  the  condenser- 
water). 

After  cooling,  the  distillate  is  filtered,  the  o-nitrophenol  washed 
with  water,  pressed  out  on  a  porous  plate,  and  dried  in  a  desic- 
cator. Since  it  is  obtained  completely  pure,  it  is  unnecessary  to 
subject  it  to  any  further  process  of  purification.  In  order  to 
obtain  the  non-volatile  p-nitrophenol  remaining  in  the  flask,  the 
mixture  is  cooled  by  immersion  in  cold  water,  the  water  solution 
is  filtered  from  the  undissolved  portions,  and  the  filtrate  boiled  for 
a  quarter-hour  with  20  grammes  of  animal  charcoal,  the  water 
evaporating  being  replaced  by  a  fresh  quantity.  The  charcoal  is 
then  filtered  off  and  the  filtrate  allowed  to  stand  in  a  cool  place 
over  night,  upon  which  the  p-nitrophenol  separates  out  in  long, 
almost  colourless  needles.  The  oil  still  present  in  the  distillation 
flask  is  boiled  with  a  mixture  of  i  part  by  volume  of  concentrated 


AROMATIC  SERIES  297 

hydrochloric  acid  and  2  parts  by  volume  of  water,  with  the  addi- 
tion of  animal  charcoal,  filtered  after  partial  cooling  and  the  ni- 
trate allowed  to  stand  over  night.  There  is  thus  obtained  a 
second  crystallisation.  If  the  crystals  which  have  separated  out 
are  still  contaminated  by  the  oil,  they  are  recrystallised  from 
dilute  hydrochloric  acid  with  the  use  of  animal  charcoal. 

Melting-point  of  o-Nitrophenol,    45° ; 
Melting-point  of  p-Nitrophenol,  1 14°. 

Yield,  30  grammes  and  5-10  grammes  respectively. 

The  mon-acid  phenols  of  the  benzene  series  are,  in  contrast  to  the 
corresponding  hydrocarbons,  very  easily  nitrated.  In  the  nitration  of 
benzene,  in  order  to  facilitate  the  elimination  of  the  water,  concen- 
trated sulphuric  acid  must  be  added ;  whereas  the  action  of  concen- 
trated nitric  acid  alone  upon  phenol  is  so  energetic,  that  in  this  case 
it  must  be  diluted  with  water.  Upon  nitrating  phenol,  the  o-  and 
p-nitrophenols  are  formed  simultaneously,  the  former  of  which  is  vola- 
tile with  steam : 

/N02 
C6H5 .  OH  -f  NO0 .  OH  =  C6H4<         +  H2O. 

NDH 

o-  and  p-Nitrophenol 

On  nitrating  the  homologues  of  phenol,  the  nitro-groups  always  enter 
the  o-  and  p-positions  to  the  hydroxyl  group.  In  order  to  prepare 
m-nitrophenol,  it  is  necessary  to  start  from  m-nitroaniline ;  this  is  diaz- 
otised  and  its  diazo-solution  boiled  with  water. 

The  nitrophenols  behave  in  all  respects  like  the  phenols.  But  by 
the  entrance  of  the  negative  nitro-group,  the  negative  character  of  the 
phenol  is  so  strengthened  that  the  nitrophenols  not  only  dissolve  in 
alkalies,  but  also  in  the  alkali  carbonates. 

EXPERIMENT:  Dissolve  some  o-nitrophenol  in  a  solution  of 
sodium  carbonate  by  warming ;  the  scarlet  red  sodium  salt  is 
formed. 

In  consequence  of  this  action,  the  nitrophenols  cannot  be  precipi- 
tated from  their  alkaline  solutions  by  carbon  dioxide. 

In  addition,  the  nitrophenols  show  the  characteristics  of  the  nitro- 
compounds  in  general,  since  they,  for  example,  pass  over  to  amido- 
phenols  on  energetic  reduction,  etc. 


298 


SPECIAL   PART 


24.   REACTION:   (a)    CHLORINATION  OF   A  SIDE-CHAIN  OF  A  HYDRO- 
CARBON,     (b)  CONVERSION  OF  A  DICHLORIDE  INTO  AN  ALDEHYDE 

EXAMPLES  :   (a)   Benzalchloride  from  Toluene 

(b)    Benzaldehyde  from  Benzalchloride 

(a)  A  joo  c.c.  round  flask  with  a  wide  neck  (Fig.  74)  con- 
taining 50  grammes  of  toluene  is  placed  in  a  well-lighted  posi- 
tion, best  in  the  sunlight.  The  toluene  is  heated  to  boiling 
and  a  current  of  dry  chlorine  conducted  into  it  until  its  weight 


FIG.  74. 

is  increased  by  40  grammes.  In  order  to  be  able  to  judge 
of  the  course  of  the  reaction,  the  flask,  with  the  toluene,  is 
weighed  before  the  experiment.  By  interrupting  the  passage  of 
the  chlorine  from  time  to  time,  cooling  and  weighing  the  flask, 
the  increase  in  weight  will  indicate  how  far  the  chlorinating  action 


AROMATIC   SERIES  299 

has  proceeded.  The  length  of  the  operation  varies  greatly.  In 
summer  the  reaction  is  complete  in  a  few  hours ;  during  the 
cloudy  days  of  winter  a  half  or  a  whole  day  may  be  necessary. 
The  reaction  may  be  materially  assisted  by  adding  4  grammes  of 
phosphorus  pentachloride  to  the  toluene. 

(^)  In  order  to  convert  the  benzalchloride  into  benzaldehyde, 
the  crude  product  thus  obtained  is  treated  in  a  round  flask  pro- 
vided with  an  effective  reflux  condenser,  with  500  c.c.  of  water 
and  150  grammes  of  precipitated  calcium  carbonate  (or  floated 
chalk  or  finely  pulverised  marble)  and  the  mixture  heated  four 
hours  in  a  hemispherical  oil-bath  to  130°  (thermometer  in  the 
oil).  Without  further  heating,  steam  is  passed  through  the  hot 
contents  of  the  flask  until  no  more  oil  distils  over.  For  this  pur- 
pose the  apparatus  necessary  (cork  with  a  glass  tube)  has  been 
prepared  before  the  heating  in  the  oil-bath. 

Before  the  crude  benzaldehyde  is  subjected  to  purification,  the 
liquid  remaining  in  the  distilling  flask  is  filtered  while  hot  through 
a  folded  filter,  and  the  filtrate  acidified  with  much  concentrated 
hydrochloric  acid.  On  cooling,  the  benzoi'c  acid  obtained  as  a 
by-product  in  the  preparation  of  benzaldehyde  separates  out  in 
lustrous  leaves.  It  is  filtered  off  and  recrystallised  from  hot  water, 
during  which  it  must  not  be  heated  too  long,  since  it  is  volatile 
with  steam.  Melting-point,  121°. 

The  oil  passing  over  with  the  steam  is  treated,  together  with  all 
of  the  liquid,  with  a  concentrated  solution  of  sodium  hydrogen 
sulphite,  until  after  long  shaking  the  greater  part  of  the  oil  has 
passed  into  solution.  Should  crystals  of  the  double  compound  of 
benzaldehyde  and  sodium  hydrogen  sulphite  separate  out,  water  is 
added  until  they  are  dissolved.  The  water  solution  is  then  filtered 
through  a  folded  filter  from  the  oil  remaining  undissolved,  and 
the  filtrate  treated  with  anhydrous  sodium  carbonate  until  it  shows 
a  strong  alkaline  reaction.  This  alkaline  liquid  is  now  subjected 
to  distillation  with  steam,  when  perfectly  pure  benzaldehyde  passes 
over ;  it  is  taken  up  with  ether,  and,  after  the  evaporation  of  the 
ether,  is  distilled.  Boiling-point,  179°. 

Under  the  preparation  of  brombenzene  it  has  already  been  men- 
tioned that  by  the  action  of  chlorine  or  bromine  on  aromatic  hydro- 
carbons containing  aliphatic  side-chains,  different  products  are  formed, 


3OO  SPECIAL   PART 

depending  on  the  temperature  at  which  the  action  takes  place.  If,  e.g^ 
chlorine  acts  at  lower  temperatures  on  toluene,  chlortoluene  is  formed, 
the  chlorine  entering  the  benzene  ring : 

/CH3 
C6H5.CH3  +  C12  =  C6H4<^        +HC1. 

At  ordinary  temperatures  Chlortoluene 

If,  on  the  other  hand,  chlorine  is  conducted  into  boiling  toluene,  the 
chlorine  atom  enters  the  side-chain : 

C6H6.CH3  +  C12  =  C6H5.CH2C1  +  HC1. 

At  boiling  temperature  Benzylchloride 

If  chlorine  is  conducted  into  toluene  at  the  boiling  temperature  for 
a  long  time,  a  second,  and  finally  a  third,  hydrogen  atom  of  the  methyl 
group  is  substituted : 

C6H5.CH2C1  +  C12  =  C6H5.CHC12  -f  HC1 

Boiling  Benzalchloride 

C6H5 .  CHC12  +  C12  =  C6H5 .  CC13     +  HC1. 

Benzotrichloride 

The  formation  of  benzotrichloride  is  the  final  result  of  the  action 
of  chlorine  under  these  conditions,  since  the  benzotrichloride  is  not 
changed  even  by  passing  in  the  chlorine  for  a  longer  time. 

The  replacement  of  hydrogen  by  chlorine  directly  presents  the  diffi- 
culty, unlike  the  liquid  bromine,  that  weighed  quantities  cannot  be 
used,  and  the  exact  point  to  which  the  introduction  of  chlorine  should 
be  continued  in  order  to  get  a  certain  definite  compound  must  be 
determined.  This  is  accomplished  if,  from  time  to  time,  the  increase 
in  weight  of  the  substance  being  chlorinated  is  determined.  Since 
the  conversion  of  one  molecule  of  toluene  to  benzylchloride  requires 
an  increase  of  weight  equal  to  the  atomic  weight  of  chlorine  minus  the 
atomic  weight  of  hydrogen  (Cl  —  H  =  34.5),  therefore  in  the  prepara- 
tion cf  benzylchloride,  100  parts  by  weight  of  toluene  must  take  up 
an  additional  weight  of  chlorine  =  37.5  parts  by  weight,  and  corre- 
spondingly in  the  preparation  of  benzalchloride  or  benzotrichloride, 
the  increase  in  parts  by  weight  must  be  respectively  2  x  37.5  =  75 
and  3  x  37.5  =  112.5. 

In  most  organic  chlorinating  reactions,  besides  the  main  reaction,  a 
side  reaction  also  takes  place  which,  in  the  above  example,  results  in 
the  conversion  of  a  portion  of  the  toluene  to  benzalchloride  and 


AROMATIC   SERIES  301 

benzotrichloride,  while  another  portion  is  only  chlorinated  to  benzyl 
chloride.  Accordingly  the  reaction-product  obtained  above  consists 
essentially  of  benzalchloride  mixed  with  a  small  quantity  of  benzyl 
chloride  and  benzotrichloride. 

The  halogen  derivatives  of  the  aromatic  hydrocarbons  containing 
the  halogen  in  the  side-chain  are  in  part  liquids,  in  part  colourless  crys 
tallisable  solids,  which  are  distinguished  from  their  isomers  containing 
the  halogen  in  the  benzene  ring,  in  that  their  vapours  violently  attack 
the  mucous  membrane  of  the  eyes  and  nose.  Care  is  taken  therefore 
in  the  above  preparation  not  to  expose  the  face  to  the  vapours,  and 
further  to  prevent  the  chlorination  products  from  coming  in  contact 
with  the  hands. 

Concerning  their  chemical  properties,  these  two  isomeric  series  differ 
in  that  the  compounds  containing  the  halogen  in  the  side-chain  are  far 
more  active  than  those  in  which  the  halogen  occurs  in  the  benzene 
ring,  as  is  apparent  from  the  following  equations : 

C6H5 .  CH2C1  +  NH3  =  C6H5 .  CH2 .  NH2  +  HC1 

Benzylamine 

C6H5 .  CH2C1  +  CH3 .  COONa  -  CH3 .  CO .  OCH2 .  C6H5  +  NaCl 

Benzylacetate 

C6H5.CH2C1  +  KCN  =  C6H,,.CH2.CN  +  KC1 

Benzyl  cyanide 

The  chlorides  obtained  by  substituting  a  side-chain  are  of  importance 
for  making  certain  preparations, —  the  aromatic  alcohols,  aldehydes, 
and  acids.  On  boiling  with  water,  they  decompose,  in  accordance  with 
the  following  equations : 

(1)  C6H5.  CH2C1  +  H20  =  C6H5.CH2.OH  +  HC1 

Benzyl  alcohol 

(2)  C6H5 .  CHC12  +  H2O  =  C6H5 .  CHO  +  2  HC1 

Benzaldehyde 

(3)  C(;H . .  CC13  +  2  H20  =  C6H5 .  CO  .  OH  +  3  HC1 

Benzo'ic  acid 

If  the  halogen  atom  is  in  the  ring,  none  of  these  transformations  will  take 
place.  But  since,  in  cases  i  and  2,  the  hydrochloric  acid  formed  in  the  re- 
action acts  in  the  opposite  way  and  may  regenerate  the  original  chloride,  it 
must  be  neutralised.  This  is  usually  accomplished  by  the  addition  of  a 
carbonate,  upon  which  the  acid  acts  with  the  liberation  of  carbon  dioxide, 


302  SPECIAL  PART 

In  practice,  the  cheap  calcium  carbonate  (marble  dust)  is  used,  and  the 
above  method  for  the  preparation  of  benzaldehyde  is,  as  far  as  possible, 
an  imitation  of  the  technical  process  used  for  obtaining  the  substance. 
From  benzylchloride,  benzaldehyde  may  also  be  prepared  directly  by 
boiling  it  with  water  in  the  presence  of  lead  nitrate  or  copper  nitrate. 
From  the  benzylchloride,  benzyl  alcohol  is  first  formed,  which  is  oxi- 
dised by  the  nitrate  to  benzaldehyde. 

As  above  mentioned,  the  chlorination  product  obtained  consists 
essentially  of  benzalchloride,  mixed  with  small  amounts  of  benzyl- 
chloride  and  benzotrichloride.  If  the  mixture  is  boiled  with  water, 
with  the  addition  of  calcium  carbonate,  a  mixture  consisting  mainly  of 
benzaldehyde,  besides  benzylchloride  and  benzole  acid  —  the  latter 
being  converted  into  the  calcium  salt  by  the  carbonate  —  is  obtained. 
If  the  reaction-mixture  is  distilled  with  steam,  benzaldehyde,  benzyl 
alcohol,  and  a  small  amount  of  chlorides  which  have  not  taken  part 
in  the  reaction,  pass  over  with  the  steam,  while  the  calcium  benzoate 
remains  in  the  distillation  flask.  By  acidifying  the  residue,  the  free 
benzole  acid  may  be  obtained  as  above.  A  large  proportion  of  the 
so-called  "benzoic  acid  from  toluene"  is  obtained  in  this  way  as  a 
by-product  in  the  technical  preparation  of  benzaldehyde.  In  order  to 
separate  the  benzaldehyde  from  benzyl  alcohol,  the  chlorides,  and  other 
impurities,  advantage  is  taken  of  the  general  property  of  aldehydes  of 
uniting  with  acid  sodium  sulphite  to  form  soluble  double  compounds. 
If  the  distillate  is  shaken  with  a  solution  of  sodium  hydrogen  sulphite, 
the  aldehyde  dissolves,  while  the  impurities  remain  undissolved.  These 
are  filtered  off,  and  the  sulphite  compound  of  the  aldehyde  decomposed 
with  sodium  carbonate ;  on  a  second  distillation  with  steam,  the  pure 
aldehyde  passes  over. 

The  aromatic  aldehydes  are  in  part  liquids,  in  part  solids,  possessing 
a  pleasant  aromatic  odour. 

They  show  the  characteristic  aldehyde  reactions,  yielding  primary 
alcohols  on  reduction  and  carbonic  acids  on  oxidation, 

EXPERIMENT:  A  few  drops  of  benzaldehyde  are  allowed  to 
stand  in  a  watch-glass  in  the  air.  After  a  long  time,  crystals  of 
benzo'ic  acid  appear. 

C6H5.CHO  +  O  =  C6H5.CO.OH. 

That  they  unite  with  acid  sulphites  to  form  crystalline  compounds  has 
been  mentioned : 


AROMATIC   SERIES  303 

/OH 
C6H5.CHO  4-  HS03Na  =  C6H5.CH 

\SO3Na 

EXPERIMENT  :  To  \  c.c.  of  benzaldehyde  add  a  concentrated 
solution  of  sodium  hydrogen  sulphite,  and  shake.  The  mixture 
solidifies  after  a  short  time  to  a  crystalline  mass. 

Further,  the  aldehydes  react,  as  mentioned  under  acetaldehyde,  with 
hydroxylamine  and  phenyl  hydrazine,  to  form  oximes  and  hydrazones. 
With  hydrazine  they  yield,  according  to  the  experiment  conditions,  the 
not  very  stable  hydrazines  or  the  more  stable  and  characteristic  azines : 

C6H5 .  CH  |O+H2|  N  -  NH2  =  H2O  +  C6H5 .  CH=N .  NH2 

Benzalhydrazine 

C6H5 .  CH  |O  +  H2|  N  C6H5 .  CH=N 

. =  2  H2O  +  | 

CfiH,.CH|O  +  H,|N  C6H5.CH=N 

Benzalazine 

Aldehydes  also  condense  readily  with  primary  aromatic  bases  with  the 
elimination  of  water : 

C6H5 .  CHO  +  C6H5 .  NH2  =  C6H5 .  CH=N  .  C6H5  +  H2O 

Benzylideneaniline 

EXPERIMENT  :  In  a  test-tube  make  a  mixture  of  i  c.c.  of  benzal- 
dehyde and  i  c.c.  of  pure  aniline,  and  warm  gently.  On  cooling, 
drops  of  water  separate  out,  and  the  mixture  solidifies,  crystals  of 
benzylideneaniline  being  formed. 

An  additional  number  of  characteristic  aldehyde  reactions  will  be 
taken  up  later  in  practice.  Benzaldehyde  is  prepared  technically  on 
the  large  scale.  Its  most  important  application  is  for  the  manufacture 
of  the  dyes  of  the  Malachite  Green  series,  and  of  cinnamic  acid  (see 
these  preparations). 

25.  REACTION:  SIMULTANEOUS  OXIDATION  AND  REDUCTION  OF 
AN  ALDEHYDE  UNDER  THE  INFLUENCE  OF  CONCENTRATED 
POTASSIUM  HYDROXIDE 

EXAMPLE  :   Benzoic  Acid  and  Benzyl  Alcohol  from  Benzaldehyde1 

Treat  20  grammes  of  benzaldehyde  in  a  stoppered  cylinder  or  a 
thick-walled  vessel  with  a  cold  solution  of  18  grammes  of  potas- 
sium hydroxide  in  1 2  grammes  of  water,  and  shake  until  a  perma- 
nent emulsion  is  formed ;  the  mixture  is  then  allowed  to  stand 
over  night.  The  vessel  is  closed  by  a  cork,  and  not  a  glass 
stopper,  since  at  times  a  glass  stopper  becomes  so  firmly  fastened 
that  it  can  be  removed  only  with  great  difficulty.  To  the  crys- 

1  B.  14,  2394. 


304  SPECIAL'  PART 

talline  paste  (potassium  benzoate)  separating  out,  water  is  added 
until  a  clear  solution  is  obtained  from  which  the  benzyl  alcohol  is 
extracted  by  repeatedly  shaking  with  ether.  After  the  evapora- 
tion of  the  ether  the  residue  is  subjected  to  distillation  ;  benzyl 
alcohol  passes  over  at  206°.  Yield,  about  8  grammes.  The  ben- 
zoi'c  acid  is  precipitated  from  the  alkaline  solution  on  acidifying 
with  hydrochloric  acid. 

While  many  aliphatic  aldehydes  (see  acetaldehyde)  are  converted 
by  alkalies  into  more  complex  compounds,  with  higher  molecular 
weights,  the  so-called  aldehyde  resins,  the  aromatic  aldehydes  under 
similar  conditions  react  smoothly  ;  two  molecules  are  decomposed  by 
one  molecule  of  potassium  hydroxide,  one  aldehyde  molecule  being 
oxidised  to  the  corresponding  acid,  and  the  other  being  reduced  to  a 
primary  alcohol  : 

2C,,H5.CHO  +  KOH  =C(;H,.CO.OK  +  CCH,.  CH2.  OH. 

Since  the  aldehydes  are  in  part  easily  obtained,  the  different  primary 
alcohols  may  be  prepared  advantageously  by  this  reaction. 

The  primary  aromatic  alcohols  behave  in  all  respects  like  the  corre- 
sponding aliphatic  alcohols  in  forming  ethers  and  esters,  e.g.  : 

C,H,.CH2\  CfiH..CH2\ 

2\0  20          CH.CO.OCR,.CH 


Benzyl  ether  Benzylmethyl  ether  Aceticbenzyl  ester 

On  oxidation  they  are  converted  first  into  aldehydes  and  finally  into 
acids  : 

C6H..CH2.OH  +  O  -  C0H5.CHO  +  H2O, 
02  =  CfiH5  .  COOH  +  H2O. 


26.   REACTION:    CONDENSATION  OF   AN  ALDEHYDE  BY  POTASSIUM 
CYANIDE  TO  A  BENZOIN 

EXAMPLE  :  Benzoin  from  Benzaldehyde l 

Mix  10  grammes  of  benzaldehyde  with  20  grammes  of  alcohol 
and  treat  the  mixture  with  a  solution  of  2  grammes  of  potassium 
cyanide  and  5  c.c.  of  water.  Boil  on  the  water- bath  for  one  hour 
(reflux  condenser).  The  hot  solution  is  poured  into  a  beaker 
and  allowed  to  cool  slowly  •  the  crystals  separating  out  are  filtered 

i  A.  198, 150. 


AROMATIC   SERIES  305 

off,  washed  with  alcohol,  and  dried  on  the  water-bath.  For  con- 
version into  benzil  (see  next  preparation),  they  need  not  be  re- 
crystallised.  In  order  to  obtain  perfectly  pure  benzoin,  a  small 
portion  of  the  crude  product  is  recrystallised  from  a  little  alcohol 
in  a  test-tube.  Melting-point,  134°.  Yield,  about  90%  of  the 
theory. 

If  an  aromatic  aldehyde  of  the  type  of  benzaldehyde  is  warmed  in 
alcohol  solution  with  a  small  quantity  of  potassium  cyanide,  substances 
are  obtained  which  possess  the  same  composition,  but  with  double  the 
molecular  weight  of  the  aldehyde  : 

C6H5.CO.CH-C6H5 
2C6H5.CHO=  | 

OH 

Benzoi'n 

This  is  unlike  aldol  formation,  since  here  condensation  takes  place 
between  the  two  aldehyde  groups  (p.  174). 

In  the  same  way  from  anisic  aldehyde  and  cuminol,  there  are  obtained 
aniso'in  and  cuminoin,  respectively  : 


yOCH3  =  CH3O  .  C6H4 .  CO  .  CH  .  C6H4 .  OCH3 
\CHO  OH 

Idehyde  Aniso'in 

C3Hr    =  C3H7 .  C6H4 .  CO .  CH— C6H4 .  C3H7. 


2P-C6H/ 

\CHO  OH 

Cuminol  Cuminoin 

With  potassium  cyanide  furfurol  yields  furoi'n : 

C4H3O  .  CO .  CH  .  C4H3O 
2  C4H30 .  CHO  = 

Furfurol  OH 

Furo'in 

Benzoin  and  its  analogues  are  derivatives  of  the  hydrocarbon  di- 
benzyl,  C,;H3.  CH2.  CH2.C6H5,  and  in  fact  benzoin  on  reduction  with 
hydriodic  acid  is  converted  into  this  hydrocarbon. 

The  benzoins  act,  on  the  one  hand,  like  ketones  if  the  carbonyl 
group  (CO)  takes  part  in  the  reaction,  and,  on  the  other  hand,  like 
secondary  alcohols  if  the  group  CH  .  OH  (the  secondary  alcohol  group) 
reacts.  Thus  they  have  the  power  to  form  oximes  and  hydrazones 
with  hydroxylamine  and  phenyl  hydrazine  respectively.  If  benzoin  is 
reduced  with  sodium  amalgam,  the  ketone  group  is  converted  into  the 
secondary  alcohol  group. 

* 


306  SPECIAL  PART 

C6H5 .  CO .  CH  .  C6H5  C6H5 .  CH— CH  .  C6H5 

•f  H2  = 
OH  OH     OH 

Hydrobenzo'in 

If  the  reduction  is  effected  by  zinc  and  hydrochloric  acid  or  glacial 
acetic  acid,  the  carbonyl  group  is  not  attacked,  but  the  alcohol  group 
is  reduced  and  desoxybenzo'in  is  obtained : 

C6H5  .CO   CH  .  C6H5  _  C6H5.CO.CH2.C6H5  +  H2O, 

OH  Desoxybenzo'in 

a  compound  of  especial  interest,  because  in  it,  as  in  acetacetic  ester,  one 
of  the  two  hydrogen  atoms  of  the  methylene  group  (CH2),  in  conse- 
quence of  the  acidifying  influence  of  the  adjoining  negative  carbonyl 
and  phenyl  groups,  may  be  replaced  by  sodium  ;  with  the  sodium  com- 
pound the  same  kind  of  syntheses  may  be  effected  as  with  acetacetic 
ester : 

C6H5 .  CO .  CH  .  C6H5  C6H5 .  CO  .  CH-C6H5 

|  +IC2H5=  +NaI. 

Na  C2H5 

Sodium  desoxybenzo'in  Ethyl  desoxybenzoin 

Benzoin,  further,  acts  as  an  alcohol,  the  hydroxyl  group  being  capa- 
ble of  reacting  with  alkyl-  and  acid-radicals  to  form  ethers  and  esters. 
If  oxidizing  agents  act  on  benzoin,  the  alcohol  group  is  oxidized  to  a 
ketone  group,  as  is  the  case  with  all  secondary  alcohols : 

C6H5.CO.CH.C6H5+0 

|  =  CdH5 .  CO  .  CO .  C6H5  +  H2O. 

Dibenzoyl  =  Benzil 

The  next  preparation  will  deal  with  this  reaction. 


27.  REACTION:  OXIDATION  OF  A  BENZOIN  TO  A  BENZIL 
EXAMPLE  :  Benzil  from  Benzoin 

The  crude  benzoin  obtained  in  the  preceding  preparation  is 
finely  pulverised  after  drying,  and  heated  in  an  open  flask,  with 
frequent  shaking,  with  twice  its  weight  of  pure  concentrated  nitric 
acid,  for  \\-2  hours  on  a  rapidly  boiling  water-bath.  When  the 
oxidation  is  ended,  the  reaction -mixture  is  poured  into  cold  water ; 


AROMATIC  SERIES  307 

after  the  mass  solidifies  the  nitric  acid  is  poured  off;  it  is 
then  washed  several  times  with  water,  pressed  out  on  a  porous 
plate,  and  crystallised  from  alcohol.  After  filtering  off  the 
crystals  separating  out,  they  are  dried  in  the  air  on  several  layers 
of  filter-paper.  Melting-point,  95°.  Yield,  about  90%  of  the 
theory. 

The  equation  representing  the  oxidation  of  benzoin  to  benzil  has 
been  given  under  the  preceding  preparation.  The  analogues  of  ben- 
zoin also  give,  on  oxidation,  compounds  of  the  benzil  series.  Thus 
from  anisoin  and  cuminom,  anisil  and  cuminil  respectively  are 
obtained  : 

CH30  .  C6H4  .  CO  .CO  .  C6H4.OCH3  ;  C3H7  .  C6H4  .  CO  .  CO  .  C6H4.  C3H7. 

Anisil  Cuminil 

Benzil  acts  like  a  ketone  in  that  it  forms  oximes  with  hydroxylamine. 
The  oximes  are  of  exceptional  interest,  since  our  knowledge  of  the 
stereochemistry  of  nitrogen  proceeds  from  them.  Benzil  forms  two 
monoximes  and  three  dioximes.  The  constitution  of  these  compounds 
will  be  discussed  later,  under  the  preparation  of  benzophenone-oxime. 

On  fusion  with  potassium  hydroxide  or  by  long  heating  with  a  water 
solution  of  potassium  hydroxide,  benzil  undergoes  a  remarkable  change, 
in  that  by  taking  up  water  it  passes  over  to  the  so-called  benzilic  acid  : 

C6H5  .  CO  .  CO  .  C6H5  +  H20  -         *Sc  .  CO  .  OH. 

C6H/  | 

OH 

Diphenylglycolic  acid  = 
Benzilic  acid 

Anisil  and  cuminil  also  yield,  in  a  similar  way,  anisilic  and  cuminilic 
acids. 


28.    REACTION:   THE  ADDITION  OP  HYDROCYANIC  ACID  TO  AN 
ALDEHYDE 

EXAMPLE:  Mandelic  Acid  from  Benzaldehyde  l 
(a)    Mandelic  Nitrile 

In  a  flask  containing  13  grammes  of  finely  pulverised  100% 
potassium  cyanide,  or  an  equivalent  amount  of  the  purest  salt 

1  B.  14,  235 


308  SPECIAL  PART 

available,  pour  20  grammes  of  freshly  distilled  benzaldehyde,  and 
add  to  this  from  a  separating  funnel,  the  flask  being  cooled  with 
ice,  a  quantity  of  the  most  concentrated  hydrochloric  acid,  corre- 
sponding to  7  grammes  of  anhydrous  hydrochloric  acid  (about  20 
grammes  concentrated  acid),  drop  by  drop,  carefully,  under  a 
hood,  with  frequent  shaking.  The  reaction-mixture  is  then 
allowed  to  stand,  with  frequent  shaking,  for  one  hour,  then 
poured  into  about  5  volumes  of  water,  the -oil  washed  with  water 
several  times,  and  finally  separated  in  a  dropping  funnel.  Owing 
to  the  ease  with  which  the  nitriles  decompose,  a  further  purifica- 
tion is  not  possible.  Yield,  almost  quantitative. 

Much  better  results  are  obtained  by  preparing  mandelic  nitrile1 
thus  :  Pour  50  c.c.  of  a  concentrated  solution  of  sodium  bisulphite 
over  15  grammes  of  benzaldehyde  in  a  beaker;  stir  the  mixture 

/H 

with   a  glass    rod   until    the    addition    product    C6H5.C — OH 

\SO3Na 

solidifies  to  a  pasty  mass.  It  is  then  filtered  with  suction,  pressed 
firmly  together,  and  washed  once  with  a  little  water.  The  double 
compound  is  stirred  up  with  water  to  a  thick  paste,  and  treated 
with  a  cold  solution  of  12  grammes  potassium  cyanide  in  25 
grammes  of  water.  After  a  short  time,  very  easily  on  stirring,  the 
crystals  go  into  solution,  and  the  nitrile  appears  as  an  oil,  which  is 
separated  from  the  solution  in  a  dropping  funnel. 

(b)    Saponification  of  the  Nitrile 

The  nitrile  is  mixed  with  four  times  its  volume  of  concentrated 
hydrochloric  acid  in  a  porcelain  dish,  and  evaporated  on  the 
water-bath  until  crystals  begin  to  separate  out  on  the  upper  surface 
of  the  liquid. 

The  reaction-mixture  is  then  allowed  to  stand  over  night  in  a 
cool  place;  the  crystals  separating  out,  are  triturated  with  a  little 
water,  filtered  off  with  suction,  and  then  washed  with  not  too 
much  water.  A  further  quantity  of  the  acid  may  be  obtained  by 


i  Ch.  Z.  1896, 90. 


AROMATIC  SERIES  309 

extracting  the  filtrate  with  ether ;  after  evaporating  off  the  ether, 
the  residue  is  heated  in  a  watch-crystal  some  time  on  a  water- 
bath.  The  crude  mandelic  acid  is  pressed  out  on  a  porous  plate, 
and  is  obtained  pure  by  recrystallising  it  from  benzene.  Melting- 
point,  1 1 8°.  Yield,  about  10-15  grammes. 

(c)    Separation  of  the  Inactive  Mandelic  Acid  into  its  Active 
Components 1 

A  mixture  of  20  grammes  of  crystallised  cinchonine,  10  grammes 
of  crystallised  mandelic  acid,  and  500  c.c.  of  water  is  heated 
with  quite  frequent  shaking  in  an  open  flask  for  an  hour  on  an 
actively  boiling  water-bath.  After  cooling,  the  portions  undis- 
solved  are  filtered  off,  and  are  not  washed.  To  this  clear  solution 
(a)  add  a  few  crystals  of  d-cinchonine  mandelate  (see  below),  and 
allow  it  to  stand,  according  to  the  conditions,  one  or  more  days  in 
a  cool  place  (6-8°;  in  summer  in  a  refrigerator,  in  winter  in  a 
cellar  if  necessary).  In  order  to  purify  the  crude  d-cinchonine 
mandelate  separating  out,  it  is  filtered  off  (filtrate  A),  pressed  out 
on  a  porous  plate,  and  recrystallised  from  water,  using  for  each 
gramme  of  the  dried  salt  25  c.c.  of  water  (heating  as  above 
described  for  an  hour,  with  quite  frequent  shaking,  in  an  open 
flask  upon  a  water-bath).  On  filtering  the  cold  solution  the  un- 
dissolved  portions  remaining  are  not  washed.  If  the  solution  be 
seeded  with  a  few  crystals  of  d-cinchonine  mandelate  and  allowed 
to  stand  under  the  same  conditions  referred  to  above,  a  purer  salt 
will  crystallise  out.  To  obtain  the  free  dextro-mandelic  acid  the 
purified  salt  is  dissolved  in  not  too  much  water,  and  then  treated 
with  a  slight  excess  of  ammonia,  which  precipitates  the  chincho- 
nine ;  this  is  filtered  off,  and,  after  recrystallisation  from  diluted 
alcohol,  may  be  used  for  other  experiments.  The  filtrate,  which 
contains  dextro-ammonium  mandelate,  is  acidified  with  hydro- 
chloric acid  and  extracted  with  ether.  If  the  residue  obtained  on 
evaporating  the  ether  be  heated  in  a  watch-glass  some  time  on  a 
water-bath,  then,  on  cooling,  crystals  of  dextro-mandelic  acid 

1  B.  16,  1773 ;  32,  2385. 


310  SPECIAL  PART 

separate  out ;  they  are  pressed  out  on  a  porous  plate  and  recrys* 
tallised  from  benzene.  Melting-point,  133-134°. 

The  pure  laevo-mandelic  cannot  be  obtained  readily  from  small 
quantities  of  mandelic  acid ;  but  a  preparation  showing  to  a  slight 
extent  laevo-rotatory  power  may  be  obtained  in  the  following  way  : 
The  filtrate  A  is  worked  up  for  the  free  acid  exactly  as  in  the 
method  described  for  pure  dextro-cinchonine  mandelate ;  since  a 
portion  of  the  d-modification  has  been  removed  from  the  solution, 
it  should  be  laevo-rotatory. 

From  the  three  preparations  thus  obtained,  viz.  inactive  mandelic 
acid,  the  pure  d-acid,  and  the  impure  1-acid,  water  solutions  of  the 
proper  concentration  are  prepared,  and  their  properties  investi- 
gated by  a  polariscope  (consult  text-books  on  Physics). 

If  one  is  not  in  possession  of  d-cinchonine  mandelate  for  the 
first  experiment,  a  proper  seeding  material  is  prepared  as  follows : 
To  a  few  cubic  centimetres  of  solution  (a)  obtained  above  is  added, 
drop  by  drop,  a  saturated  solution  of  salt  until  a  slight  precipita- 
tion takes  place.  The  solution  is  now  heated  until  the  precipitate 
redissolves,  and  is  allowed  to  stand  until  crystals  separate  out, 
which  may  require  several  days.  The  crystals  thus  obtained  are 
those  of  cinchonine  hydrochloride  upon  which  small  quantities  of 
d-cinchonine  mandelate  have  been  deposited ;  the  latter  are  in 
sufficient  quantity,  however,  to  cause  a  further  separating  out  of 
the  d-salt. 

Hydrocyanic  acid  unites  with  aromatic  as  well  as  aliphatic  aldehydes 
and  ketones  with  the  formation  of  a-oxyacid  nitriles : 

/OH 
CH3 .  CHO  +  HCN  =  CH3 .  CH< 

\CN 

Aldehydecyanhydrine 
a-lactic  nitrile 

OH 
C2H3 .  CO  .  C2H5  +  HCN  = 

-  9  11  r 

Diethylketone  Diethylglycolic  nitrile 

/OH 

C6H5 .  CHO  4-  HCN       =  CGH5 .  CH/ 

NDN 

Benzaldehyde  Mandelic  nitrile 


AROMATIC   SERIES  311 

C6H.5V      /OH 


HCN  = 

:N 

Acetophenone  Acetophenonecyanhydrine 

This  reaction  also  takes  place  with  more  complex  compounds  con- 
taining the  carbonyl  group : 

CH.3 .  CO .  CH2 .  CO  .  OC2H3  +  HCN  =  CH3 .  C— CH2 .  CO .  OC2H5 

Acetacetic  ester  /   >^ 

OH  CN 
CH3 .  CO .  CO  .  OH  +  HCN  =  CH3 .  C— CO  .  OH 

Pyroracemic  acid  /\^ 

OH   CN 

a-Cyan-a-lactic  acid 

QH5.CO.CH,.OH  +  HCN  =  C6H5.C— CH2.OH 

Benzoylcarbinol  //\^ 

OH    CN 

The  reaction  may  be  effected  by  digestion  with  already  prepared 
hydrocyanic  acid  at  ordinary  or  higher  temperatures,  but  in  most  cases 
it  is  more  advantageous  to  employ  nascent  hydrocyanic  acid  as  above. 

If  the  second  method  be  followed,  —  treating  the  aldehyde  with 
sodium  bisulphite,  —  the  reaction  takes  place  in  accordance  with  the 
following  equation  : 

OH  /OH 

C6H3.CH  =C6H5.CH       +KNaSO3 


If  the  oxynitriles  are  subjected  to  saponification,  for  example,  by 
boiling  with  hydrochloric  acid,  the  free  oxyacid  is  obtained,  e.g. : 

/OH  /OH 

C6H-.CH<         +  2  H.,0  +  HC1  =  C0H5.CH<  +  NH4C1 

>CN  \CO.OH 

Mandelic  nitrile  Mandelic  acid 

Since  the  cyanhydrine  reaction  takes  place  smoothly  in  most  cases, 
it  is  frequently  used  for  the  preparation  of  a-oxyacids. 

Thus  in  the  sugar  group  the  cyanhydrine  reaction  is  of  extreme  im- 
portance, not  only  for  its  value  in  determining  constitution,  but  also  for 
the  syntheses  of  sugars  or  sugar-like  substances  containing  long  chains 
of  carbon  atoms. 

In  reference  to  the  latter,  one  example  may  be  mentioned.     If  hydro- 


312  SPECIAL   PART 

cyanic  acid  is  united  with  grape  sugar,  which  is  an  aldehyde,  there  is 
first  obtained  an  oxynitrile,  which  on  saponification  yields  an  oxyacid. 
If  this,  or  rather  the  inner  anhydride  (lactone)  into  which  it  easily 
passes,  is  reduced,  the  carboxyl  group  is  reduced  to  an  aldehyde  group, 
and  there  is  thus  obtained  a  sugar  containing  one  more  secondary 
alcohol  (CHOH)  group  than  the  original  grape  sugar: 

CN  CO.OH 

CHO  |  CHO 

|  CH.OH  CH.OH  | 

(CH.OH)4+HCN=  |  saponified-*-  |  reduced -*-(CH.OH)5 


(CH.OH),  (CH.OH)4 

CH2.OH  |  |  CH2.UH 

CH2.OH  CH2.OH 

Aldohexose  Aldoheptos* 

With  the  substance  thus  obtained  a  similar  reaction  may  be  carried 
out,  and  so  on. 

Mandelic  acid  belongs  to  the  class  of  substances  containing  an 
asymmetric  carbon  atom,  i.e.,  one  which  is  in  combination  with  four 
different  substituents  :  ^  ^ 

*C<OH5 
\CO.OH 

Like  all  compounds  of  this  class,  it  exists  in  two  different  space 
modifications,  which  bear  the  same  relation  to  each  other  as  does  an 
object  and  its  image,  and  owing  to  their  power  of  revolving  the  plane 
of  polarisation,  are  called  dextro-  and  laevo-mandelic  acids.  The  acid 
obtained  in  the  above  synthesis  is  optically  inactive ;  since,  in  the 
synthesis  of  compounds  with  an  asymmetric  carbon  atom  from  inactive 
substances,  an  equal  number  of  molecules  of  the  dextro-  and  laevo- 
varieties  are  always  obtained,  which,  in  the  above  case,  unite  to  form 
the  inactive,  so-called,  para-mandelic  acid.  But,  by  different  methods, 
the  active  acids  can  be  obtained  from  the  inactive  modifications.  If, 
e.g.,  the  cinchonine  salt  of  para-mandelic  acid  is  allowed  to  crystallise, 
the  more  difficultly  soluble  salt  of  the  dextro-acid  separates  out  first, 
and  then,  later,  the  laevo-salt  crystallises. 

With  the  aid  of  certain  micro-organisms,  the  inactive  compounds 
may  be  decomposed  into  their  active  constituents.  If,  e.g.,  the  well- 
known  Penicillium  glaucum  is  allowed  to  grow  in  a  solution  of  ammo- 
nium para-mandelate.  it  destroys  the  laevo-modification  ;  while  another 
organism,  Saccharomyces  ellipso'ideus,  consumes  the  dextro-modification, 
and  leaves  the  other. 


AROMATIC  SERIES  313 

29.    REACTION:    PERKIN'S  SYNTHESIS  OP  CINNAMIC  ACIDi 
EXAMPLE  :    Cinnamic  Acid  from  Benzaldehyde  and  Acetic  Acid 

A  mixture  of  20  grammes  of  benzaldehyde,  30  grammes  of 
acetic  anhydride,  both  freshly  distilled,  and  10  grammes  of  anhy- 
drous pulverised  sodium  acetate  (for  the  preparation,  see  page 
147),  is  heated  in  a  flask  provided  with  a  wide  vertical  air-con- 
denser about  60  cm.  long,  for  8  hours,  in  an  oil-bath  at  180°. 
If  the  experiment  cannot  be  completed  in  one  day,  a  calcium 
chloride  tube  is  placed  in  the  upper  end  of  the  condenser  over 
night.  After  the  reaction  is  complete,  the  hot  reaction-product 
is  poured  into  a  large  flask ;  add  water,  and  then  distil  with  steam, 
until  no  more  benzaldehyde  passes  over.  The  quantity  of  water 
used  here  is  large  enough  so  that  all  of  the  cinnamic  acid  dissolves 
except  a  small  portion  of  an  oily  impurity.  The  solution  is  then 
boiled  a  short  time,  with  some  animal  charcoal,  and  filtered ;  on 
cooling,  the  cinnamic  acid  separates  out  in  lustrous  leaves.  Should 
it  not  possess  the  correct  melting-point,  it  is  recrystallised  from  hot 
water.  Melting-point,  133°.  Yield,  about  15  grammes. 

The  reaction  involved  in  the  Perkin  synthesis  takes  place  in  accord- 
ance with  this  equation : 

C6H5.CHO  +  CH3.CO.ONa  =  C6H5.CH=CH.CO.ONa+H2O. 

Sodium  cinnamate 

The  reaction,  however,  does  not  take  place,  as  appears  from  the 
equation,  by  the  direct  union  of  the  aldehyde-oxygen  atom  with  the 
hydrogen  atoms  of  the  methyl  group  and  a  combination  of  the  resulting 
residues,  but  it  proceeds  in  two  phases. 

In  the  first,  the  sodium  acetate  unites  with  the  aldehyde,  forming 
sodium  phenyl  lactate : 

C6H5.CH.CH2.CO.ONa 
(i)      C6H5.CHO  +  CHo.CO.ONa  = 

OH 

Sodium  phenyl  lactate 


1 J-  l877.  789 ;  B.  io,  68 ;  16,  14365  A.  227, 48. 


314  SPECIAL   PART 

In  the  second  phase,  this  salt,  under  the  influence  of  acetic  anhydride, 
loses  water,  upon  which  the  sodium  cinnamate  is  formed : 

(2)  C6H5.CH.CH9.CO.ONa 

=  C6H5 .  CH=CH .  CO .  ONa  +  H2O. 
OH 

That  sodium  acetate,  and  not  the.  acetic  anhydride,  condenses  with 
the  benzaldehyde,  is  proved  by  the  following  facts  :  If,  instead  of  sodium 
acetate,  sodium  proprionate  is  used,  and  this  is  heated  with  benzalde- 
hyde and  acetic  anhydride,  cinnamic  acid  is  not  obtained,  but  methyl 
cinnamic  acid : 

QH,.  CH— CH— CO .  ONa 


(1)  C6Hs.CHO  +  CH3.CH9.CO.ONa=  |          I 

OH     CH 

(2)  C6H5.CH— CH.CO.ONa      CGH5 .  CH=C— CO .  ONa  +  H2O. 

OH 


CH,  CHc 


Sodium  methyl  cinnamate 

It  follows  from  this  that  the  sodium  salt  used  always  takes  part  in 
the  reaction.  In  the  experiment  it  is  of  course  necessary  that  the 
fusion  is  not  carried  out  at  so  high  a  temperature  as  in  the  above 
'example,  but  only  at  the  heat  of  the  water-bath ;  at  higher  tempera- 
tures the  sodium  salt  of  proprionic  acid  and  acetic  anhydride  decom- 
pose into  sodium  acetate  and  proprionic  anhydride,  so  that  cinnamic 
acid  is  obtained,  and  therefore,  apparently,  the  anhydride  reacts  with 
the  aldehyde. 

The  Perkin  reaction  is  capable  of  numerous  modifications,  since  in 
place  of  benzaldehyde,  its  homologues,  its  nitro-  and  oxy-derivatives, 
etc.,  may  be  used.  On  the  other  hand,  the  homologues  of  sodium 
acetate  may  be  used  as  has  been  pointed  out.  The  condensation 
in  these  cases  always  takes  place  at  the  carbon  atom  adjoining  the 
carboxyl  group.  Halogen  substituted  aliphatic  acids  will  also  react; 
thus  from  benzaldehyde  and  chloracetic  acid,  chlorcinnamic  acid  is 
obtained : 

CfiH5.CHO  +  CH2.Cl.CO.OH  =  C6H5 .  CH=CC1 .  CO  .  OH  -f  H2O. 

In  place  of  the  aliphatic  homologues  of  acetic  acid  the  aromatic  sub« 
stituted  acetic  acids  can  also  be  used,  e.g. : 

Q.H- .  CH=C— CO  .  OH  +  H  2O. 
C6H5.CHO  +  CfiH5.CH2.CO.OH  =  | 

CCH5 

Phenyl  acetic  acid  Phenyl  cinnamic  acid 


AROMATIC  SERIES  315 

These  examples  are  sufficient  to  show  the  wide  application  of  the  Per- 
kin  reaction. 

A  very  similar  reaction  takes  place  on  heating  sodium  acetate  with 
the  cheaper  benzalchloride,  instead  of  benzaldehyde : 

C6H  5 .  CHC13  +  CH3  .  CO  .  ONa  =  C6H5 .  CH=CH  .  CO  .  ONa  +  2HC1. 

Cinnainic  acid,  its  homologues  and  analogues,  behave  on  the  one 
hand  like  acids,  since  they  form  salts,  esters,  chlorides,  amides,  etc. 
Further,  they  show  the  properties  of  the  ethylene  series  in  that  they 
take  up  by  addition  the  most  various  kinds  of  atoms  and  groups.  By 
the  action  of  nascent  hydrogen  two  atoms  of  hydrogen  are  added  to 
the  molecule  of  cinnamic  acid  with  a  change  from  double  to  single 
union : 

C6H5 .  CHizCH  .  CO  .  OH  +  H2  =  C6H5 .  CH2 .  CH2 .  CO  .  OH. 

Hydrocinnamic  acid 

It  also  combines  with  chlorine  and  bromine : 

C6H5 .  CH=CH  .  CO  .  OH  +  C12  =  C6H5 .  CHC1 .  CHC1 .  CO .  OH 

Dichlorhydrocinnamic  acid 

C6H, .  CH=CH  .  CO  .  OH  -f  Br2  =  C6H, .  CHBr .  CHBr .  CO  .  OH. 

Dibromhydrocinnamic  acid 

Further,  it  unites  with  hydrochloric,  hydrobromic,  and  hydriodic 
acids,  e.g. : 

CfiH5 .  CH=CH  .  CO .  OH  +  HBr  =  C6H- .  CHBr .  CH2 .  CO .  OH. 

/3-bromhydrocinnamic  acid 

The  halogen  atom  in  these  cases  always  unites  with  the  carbon  atom 
not  adjoining  the  carboxyl  group. 

Hypochlorous  acid  also  unites  with  cinnamic  acid  with  the  forma- 
tion of  phenylchlorlactic  acid : 

C6H5 .  CH— CHC1 .  CO  .  OH. 
C(5H, .  CH- CH  .  CO  .  OH  +  C1OH  =  | 

OH 

The  o-nitrocinnamic  acid  from  which  indigo  is  synthetically  prepared 
is  of  technical  importance.  If  cinnamic  acid,  or  better,  an  ester  of  it, 
is  nitrated,  a  mixture  of  the  o-  and  p-nitroderivatives  is  obtained 
which  can  be  separated  into  its  constituents.  If  bromine  is  allowed  to 
act  on  the  o-nitrocinnamic  acid,  there  is  obtained : 

/N02 
o-C6H4< 

\CHBr— CHBr,  CO.  OH 


3l6  SPECIAL  PART 

If  this  acid  is  boiled  with  alcoholic  potash,  two  molecules  of  hydro, 
bromic  acid  are  split  off  as  in  the  preparation  of  acetylene  from  ethyl- 
ene  bromide,  and  o-nitrophenylpropriolic  acid  is  formed,  which,  with 
alkaline  reducing  agents,  yields  indigo,  and  is  used  in  indigo  printing.' 

.NO2 
o-CgH4^ 

\C=C.CO.OH. 

Cinnamic  acid  is  known  in  two  stereoisomeric  forms : 

C6H5.C.H  C6H5.CH 


H.L 


CO. OH  HO.OC.CH 

(Cinnamic  acid)  (Allocinnamic  acid) 

Trans-form  Cis-form 


30.    REACTION:    ADDITION  OF  HYDROGEN   TO  AN  ETHYLENE 
DERIVATIVE 

EXAMPLE:    Hydrocinnamic  Acid  from  Cinnamic  Acid 

In  a  glass-stoppered  cylinder,  or  a  thick-walled  preparation  glass, 
treat  10  grammes  of  cinnamic  acid  with  75  c.c.  of  water;  add  a 
very  dilute  solution  of  caustic  soda  until  the  acid  passes  into  solu- 
tion and  the  liquid  is  just  alkaline.  If  a  precipitate  of  sodium 
cinnamate  separates  out  at  this  point,  too  much  caustic  soda  has 
been  used.  It  is  then  treated  gradually  with  about  200  grammes 
of  2  %  sodium  amalgam,  and  heated  gently,  as  soon  as  this  has 
become  liquid,  on  the  water-bath  for  a  short  time.  The  liquid  is 
then  decanted  from  the  mercury  and  acidified  with  hydrochloric 
acid,  upon  which  the  hydrocinnamic  acid  separates  out  as  an  oil ; 
when  cooled  with  ice-water  and  rubbed  with  a  glass  rod,  it  solidifies 
to  a  crystalline  mass.  After  pressing  it  out  on  a  porous  plate,  the 
acid  is  recrystallised  from  water.  Since  it  possesses  a  low  melting- 
point,  it  may  separate  out  as  an  oil  on  cooling,  in  which  case  pro- 
ceed according  to  the  directions  given  on  page  8.  Melting-point, 
47°.  Yield,  8-9  grammes. 

The  equation  for  the  reaction  has  been  given  under  cinnamic  acid. 
The  same  reaction  also  takes  place  on  heating  with  hydriodic  acid  and 
red  phosphorus. 


AROMATIC  SERIES 


31.    REACTION:    PREPARATION    OF    AN    AROMATIC    ACID-CHLORIDE 
FROM  THE   ACID  AND   PHOSPHORUS   PENTACHLORIDE 

EXAMPLE  :    Benzoyl  Chloride  from  Benzoic  Acid 1 

Treat  50  grammes  of  benzoic  acid  in  a  dry  J-litre  flask,  with  90 
grammes  of  finely  pulverised  phosphorus  pentachloride  under  the 
hood  ;  the  two  are  shaken  well  together,  upon  which,  after  a  short 
time,  reaction  takes  place  with  energetic  evolution  of  hydrochloric 
acid,  and  the  mass  becomes  liquid.  In  order  to  prevent  the 
vessel,  which  has  become  strongly  heated  by  the  reaction,  from 
cracking,  it  is  not  placed  on  the  cold  stone  floor  of  the  hood,  but 
on  a  wooden  block  or  straw  ring.  After  standing  a  short  time, 
it  is  gently  heated  on  a  water-bath,  and  the  completely  liquid 
mixture  is  twice  fractionated  (under  the  hood)  with  the  use 
of  an  air  condenser,  observing  the  directions  given  on  pages 
24  and  25.  Boiling-point  of  benzoyl  chloride,  200°.  Yield, 
90  %  of  the  theory. 

The  formation  of  benzoyl  chloride  takes  place  in  accordance  with 
the  following  reaction  : 

C6H, .  CO  .  OH  +  PCI.,  =  CCH5 .  CO .  Cl  +  POC13  +  HC1 

It  has  been  mentioned  under  acetyl  chloride  that,  for  the  preparation 
of  the  aromatic  acid-chlorides,  phosphorus  pentachloride  is  generally 
used.  Benzoyl  chloride  differs  from  acetyl  chloride  in  that  it  is  more 
difficultly  decomposed  by  water. 

EXPERIMENT  :  Treat  £  c.c.  of  benzoyl  chloride  with  5  c.c.  of 
water  and  shake.  While  acetyl  chloride,  under  these  conditions, 
decomposes  violently,  the  benzoyl  chloride  is  scarcely  changed. 
It  is  then  warmed  somewhat.  It  must  be  subjected  to  a  longer 
heating  before  all  the  oil  has  been  decomposed. 

In  other  respects,  benzoyl  chloride  is  a  wholly  normal  acid-chloride, 
and  what  was  said  under  acetyl  chloride  is  applicable  to  this  chloride ; 
only  it  is  'possible  to  prepare  aromatic  amides  by  a  different  method 
from  that  used  for  the  preparation  of  acetamide. 


1  A.  3,  262.    Ostwald's  Klassiker  der  exakten  Wissenschaften,  Nr.  22.     (Investi- 
gations concerning  the  Radical  of  Benzoic  Acid,  by  Wohler  and  Liebig.) 


3l8  SPECIAL  PART 

EXPERIMENT  :  In  a  porcelain  dish,  10  grammes  of  finely  pulver- 
ised ammonium  carbonate  are  treated  with  5  grammes  of  benzoyl 
chloride ;  they  are  intimately  mixed  with  a  glass  rod  and  heated 
on  the  water-bath  until  the  odour  of  the  acid-chloride  has  van- 
ished. The  mixture  is  then  diluted  with  water,  filtered  with  suction, 
washed  with  water,  and  crystallised  from  water.  Melting-point  of 
benzamide,  128°. 

C6H5 .  CO .  Cl  +  NH3  =  C6H5 .  CO .  NH2  +  HC1 


32.  REACTION:  THE  SCHOTTEN-BAUMANN  REACTION  FOR  THE 
RECOGNITION  OF  COMPOUNDS  CONTAINING  THE  AMIDO-,  IMIDO-, 
OR  HYDROXYL-GROUP 

EXAMPLE  :  Benzoicphenyl  Ester  from  Phenol  and  Benzoylchloride  1 

Dissolve  a  small  quantity  of  crystallised  phenol  (about  ^  gramme) 
in  5  c.c.  of  water  in  a  test-tube  and  add  \  c.c.  of  benzoyl  chloride  ; 
make  the  solution  alkaline  with  a  solution  of  caustic  soda  and,  with 
shaking,  heat  gently  a  short  time  over  a  free  flame.  If  the  reac- 
tion-mixture is  cooled  by  water  and  then  shaken  and  the  sides  of 
the  tube  rubbed  with  a  glass  rod,  the  oil  separating  out  solidifies 
to  colourless  crystals,  which  are  filtered  off  with  suction,  washed 
with  water,  pressed  out  on  a  porous  plate,  and  recrystallised  in  a 
small  test-tube  from  a  little  alcohol.  Melting-point,  68-69°. 

As  already  mentioned  under  acetyl  chloride,  acid-chlorides  react  with 
alcohols,  phenols,  primary  and  secondary  amines,  the  chlorine  atom 
uniting  with  the  hydrogen  of  the  hydroxyl-,  amido-,  or  imido-group, 
with  the  elimination  of  hydrochloric  acid,  while  the  residues  combine 
to  form  an  ester  or  a  substituted  amide.  The  value  of  the  Schotten- 
Baumann  reaction  depends  on  the  fact  that  this  reaction  is  so  essen- 
tially facilitated  by  the  presence  of  sodium  hydroxide  or  potassium 
hydroxide,  that  even  in  the  presence  of  water  the  decomposition  takes 
place. 

5.CO.Cl  +  NaOH=C6H5.O.OC.C6H5+NaCl  +  H2O 


l  B.  19,  3218  ;  21,  2744;  23,  2962;  17,  2545. 


AROMATIC   SERIES  319 

The  reaction  is  of  great  importance,  especially  for  the  recognition  and 
characterisation  of  soluble  compounds  containing  the  groups  mentioned 
above.  It  is  obvious  that  if  it  is  desired  to  test  even  small  quantities 
of  those  compounds,  the  most  difficultly  soluble  acid  derivatives  of 
them  must  be  prepared.  The  benzoyl  derivatives  are  particularly  well 
adapted  to  this  purpose.  A  few  examples  may  render  this  statement 
clearer  :  If  a  water  solution  of  a  poly-acid  aliphatic  alcohol,  e.g., 
glycerol,  or  of  the  various  sugars,  from  which  the  dissolved  substance 
will  only  separate  with  difficulty,  is  treated  with  benzoyl  chloride  and 
alkali,  a  benzoate  is  formed,  which  is  generally  insoluble  in  water,  and 
which  can  be  recognised  by  its  melting-point.  For  the  recognition  of 
primary  and  secondary  amines  the  method  of  procedure  is  the  same. 
Thus,  e.g-,  it  is  not  difficult  to  convert  aniline  (one  drop  dissolved  in 
water)  by  the  above  method  to  benzanilide,  which  can  be  recognised 
by  its  melting-point,  163°.  (Try  the  experiment.) 


The  soluble  amido-phenols,  di-  and  poly-amines  are  also  converted 
into  difficultly  soluble  benzoyl  derivatives  : 

/NH2  /NH.CO.CeH5 

Ct;H4<          +  2  C6H,  .  CO  .  Cl  =  C6H4<  +  2  HC1 

\OH  \O.OC.C6H3 

/NH,  /NH.CO.QH, 

CfJH4<        "  +  2  CflH  ,  .  CO  .  Cl  =  C6H4<  +2  HC1. 

\NH2  \NH.CO.C6H5 

In  place  of  benzoyl  chloride,  other  chlorides,  e.g.,  phenylacetyl  chloride, 
or  benzenesulphon  chloride,  can  be  used,  which  act  in  a  similar  way. 
Acetyl  derivatives  may  also  be  prepared  in  the  presence  of  alkalies  in 
water  solution,  only  in  this  case  acetic  anhydride  and  not  the  easily 
decomposed  acetyl  chloride  is  used.  At  times  the  reaction  takes  place 
better  by  using-  potassium  hydroxide,  or  pyridine,  in  place  of  sodium 
hydroxide. 


320  SPECIAL   PART 


33.   REACTION:    (a)    PRIEDEL    AND    CRAFTS'    KETONE    SYNTHESIS  1 
(*)   PREPARATION    OF    AN  OXIME 
(e)   BECKMANN'S  TRANSFORMATION  OF  AN  OXIME 

EXAMPLE  :    Benzophenone    from    Benzoylchloride,   Benzene    and 
Aluminium  Chloride 

(a)  To  a  mixture  of  30  grammes  of  benzene,  30  grammes  of 
benzoyl  chloride,  and  100  c.c.  (=  130  grammes)  cf  carbon  disul- 
phide  in  a  dry  flask,  add,  in  the  course  of  about  10  minutes,  with 
frequent  shaking,  30  grammes  of  freshly  prepared  and  finely  pulver- 
ised aluminium  chloride,  which  is  weighed  in  a  dry  test-tube  closed 
by  a  cork.  The  flask  is  then  connected  with  a  long  reflux  con- 
denser, and  heated  on  a  gently  boiling  water-bath  (a  water-bath 
heated  to  50°  is  better)  until  only  small  amounts  of  hydrochloric 
acid  are  evolved  :  this  will  require  about  2-3  hours.  The 
carbon  disulphide  is  then  distilled  off,  and  the  residue,  while 
still  warm,  is  carefully  poured  into  a  large  flask  containing 
300  c.c.  of  water  and  small  pieces  of  ice.  The  residue  adher- 
ing to  the  walls  of  the  first  flask  is  treated  with  water,  and 
the  water  added  to  the  main  quantity.  After  the  reaction-mixture 
has  been  treated  with  10  c.c.  of  concentrated  hydrochloric  acid, 
steam  is  passed  into  it  for  about  a  quarter-hour.  The  residue 
remaining  in  the  flask  is,  after  cooling,  extracted  with  ether,  the 
ethereal  solution  washed  several  times  with  water,  filtered,  and 
shaken  up  with  dilute  caustic  soda  solution.  After  drying  with 
calcium  chloride,  the  ether  is  evaporated,  and  the  residue  distilled 
from  a  fractionating  flask,  the  side-tube  of  which  is  as  near  as  pos- 
sible to  the  bulb.  Boiling-point,  297°.  Melting-point,  48°.  Yield, 
about  30  grammes. 

(<£)  A  solution  of  2  grammes  of  benzophenone  in  15  c.c.  of  al- 
cohol is,  with  cooling,  treated  with  a  cold  solution  of  1.5  grammes 
of  hydroxylamine  hydrochloride  in  5  c.c.  of  water,  and  3.5 
grammes  of  caustic  potash  in  6  grammes  of  water ;  the  mixture 
is  heated  two  hours  on  the  water-bath,  with  a  reflux  condenser. 
Then  add  50  c.c.  of  water,  and  filter  off,  if  necessary,  any  un* 

1  A.  ch.  [6]  i,  518. 


AROMATIC  SERIES  32! 

changed  ketone  which  balls  together  very  easily  on  shaking; 
acidify  the  filtrate  slightly  with  dilute  sulphuric  acid,  and  recrys- 
tallise  the  free  oxime  from  alcohol.  Melting-point,  140°. 

(c)  A  weighed  amount  of  the  oxime  is  dissolved  in  some 
anhydrous,  alcohol-free  ether,  at  the  ordinary  temperature,  and 
gradually  treated  with  i^-  times  its  weight  of  finely  pulverised 
phosphorus  pentachloride.  The  ether  is  then  distilled  off,  the 
residue,  with  cooling,  is  treated  with  water,  and  the  precipitate 
separating  but  is  recrystallised  from  alcohol.  Melting-point,  163°. 

(a)  If  an  aromatic  or  an  aliphatic  acid-chloride  is  allowed  to  act  on 
an  aromatic  hydrocarbon  in  the  presence  of  an  anhydrous  aluminium 
chloride,  one  of  the  benzene-hydrogen  atoms  will  be  replaced  by  an 
acid  radical,  a  ketone  being  formed  : 

C6H6  +  C6H5  .  CO  .  Cl  -  C6H3  .  CO  .  C6H5  +  Hd 

Diphenyl  ketone 
=Benzophenone 

C6H6  +  CH3  .  CO  .  Cl  =  C6H,  .  CO  .  CH3  +  HC1. 

Phenylmethyl  ketone 
=Acetophenone 

The  reaction  may  be  varied  if  (i)  in  place  of  benzene  a  homologue  is 

used: 

/CH3 

C6H5.CH3  +  C6H5.CO.C1  =  p-C6H/  +  HC1. 

\CO.C6H5 

Toluene  Phenyltolyl  ketone 

[n  cases  of  this  kind,  the  acid-radical  always  enters  the  para  position 
to  the  alkyl  radical.  If  this  is  already  occupied,  it  then  goes  to  the 
ortho  position.  (2)  In  place  of  hydrocarbons,  phenol-ethers,  which 
react  with  extreme  ease,  can  be  used  : 

/OCH3 

C6H3  .  OCH3  +  C6H5  .  CO  .  Cl  =  C6H/  +  HC1. 

\CO.C6H5 

Anisol  Anisylphenyl  ketone 

Concerning  the  entrance  of  the  acid-radical,  the  statements  made  above 
are  also  true  for  this  case.  (3)  In  place  of  ben-zoyl  chloride  or  acetyl 
chloride,  their  homologues  can  be  used  : 

/CH3 
C6H6  +  C6H4<  =  C6H6.CO.C6H4.CH3  +  HC1 


Toluyl  chloride 


322  SPECIAL  PART 

C,H6  +  CH3 .  CH2 .  CO .  Cl  =  C6H5 .  CO .  CH2 .  CH3  +  HC1 
C6H6  +  C6H5 .  CH2 .  CO .  Cl  =  C6H5 .  CO .  CH2 .  C6H5  +  HC1. 

;' benzyl  ketom 
soxybenzo'in 


Phenylacetyl  chloride  Phenylbenzyl  ketone  = 

des 


In  this  way,  starting  from  o-  or  m-toluic  acid,  the  o-  or  m-tolyl- 
phenyl  ketone  can  be  prepared ;  it  cannot  be  obtained  by  the  action  of 
benzoyl  chloride  on  toluene.  (4)  Substituted  acid-chlorides  like 
brombenzoyl  chloride,  nitrobenzoyl  chloride,  etc.,  can  be  used,  and 
thus  halogen  or  nitroketones  are  obtained: 


CGH6  +  C6H  /  =  C6H5 .  CO .  C6H4 .  Br  +  HC1 

CO  .  Cl  Brombenzophenone 

Brombenzoyl  chloride 

/N02 
C6H6  +  C6H  /  =  C6H5 .  CO .  C6H4 .  NO2  +  HC1. 

CO  .  Cl  Nitrobenzophenone 


jphenor 
Nitrobenzoyl  chloride 

(5)  Finally,  the  chlorides  of  dibasic  acids  react  with  the  formation  of 
diketones  or  ketonic  acids  : 

CH9— CO .  Cl  CH9 .  CO .  C6H5 

|  +2C6H6=|  +2HC1 

CH2-CO.C1  CH2.CO.C6H5 

Succinic  chloride 

/CO.C1  /CO.C6H5 

m-  and  p-C6H4<  +  2  CGH6  =  C6H4<  +  2  HC1 

XTO.Cl  \CO.C6H5 

Iso-  and  tere-phthalyl  chloride 


CO     +  2  C6H6  =  C6H5 .  CO .  C6H5  +  2  HC1. 

>Q 

Phosgene  Benzophenone 

In  these  reactions  if  but  one  chlorine  atom  should  react,  the  chlorides 
of  the  three  following  acids  would  be  obtained : 

CH2.CO.C6H5  /CO.QH5 

CM/  ,         C6H5.CO.OH. 


CH2.CO.OH  \CO.OH  "Benzotcacid 

Benzoylproprionic  acid  Benzoylbenzoic  acid 


AROMATIC   SERIES  323 

From  the  chloride  of  phthalic  acid  phthalophenone  is  formed,  im- 
portant on  account  of  its  relation  to  the  fluorescei'h  dyes : 

CCL 


+  2  C6H6  =  C6H4<         >0  +  2  HC1. 
XX)  / 

Phthalophenone 

Michler's  ketone,  tetramethyldiamidobenzophenone  is  of  technical 
importance ;  it  is  obtained  from  dimethyl  aniline  and  phosgene,  and  is 
used  in  the  preparation  of  dyes  of  the  fuchsine  series  (see  Crystal 
Violet) : 

x?ift.N(cii£fl 

2  C6H5.  N(CH3)2  +  COC12  =  CO  +2  HC1. 

\C6H4.N(CH3)2 

The  Friedel-Crafts  reaction  can  also  be  used  for  the  preparation  of 
,the  homologous  aromatic  hydrocarbons,  since  in  place  of  the  acid- 
chloride,  halogen  alkyls  may  be  caused  to  act  on  the  hydrocarbons : 1 

C6H6  +  C2H5Br  =  C6H5.C2H5  +  HBr 

/CH3 

C6H5 .  CH3  +  CH3C1  =  C6H4<          +  HC1. 

\CH3 

Toluene  Xylene 

But  in  this  connection  the  reaction  is  in  many  cases,  and  indeed  in 
the  simplest  case,  not  of  equal  importance  with  its  application  for  the 
ketone  syntheses,  for  three  reasons :  First,  the  product  of  the  reaction 
is  a  hydrocarbon  which  can  again  react;  thus  it  is  often  difficult  to 
limit  the  reaction  to  the  desired  point.  For  example,  in  the  action  of 
methyl  chloride  on  toluene,  not  only  is  one  hydrogen  atom  substituted, 
with  the  formation  of  dimethyl  benzene,  but  varying  quantities  of  tri-, 
tetra-,  penta-,  and  hexa-methyl  benzene  are  also  formed.  A  second 
disadvantage  is  this:  In  the  different  series  a  mixture  of  isomers  is 
obtained;  in  the  above  case,  e.g.,  not  only  one  of  the  three  dimethyl 
benzenes,  but  a  mixture  of  the  o-,  m-,  and  p-varieties  is  formed,  which 
cannot  be  separated  like  the  homologues  by  fractional  distillation. 
The  reaction  is  still  further  complicated  in  that  the  aluminium  chloride 
partially  splits  off  the  alkyl  groups : 

C6H5 .  CH3  +  HC1  =  C6H6  +  CH3C1. 
i  B.  14,  2627. 


324 


SPECIAL  PART 


Since  the  lower  homologues  thus  formed  again  react  synthetically  with 
the  halogen  alkyls,  and  the  halogen  alkyls  on  elimination  also  take  part 
in  the  reaction,  mixtures  often  difficult  to  separate  are  formed.  In 
some  favourable  cases  the  reaction  is  of  use  in  the  preparation  of  the 
homologues  of  benzene.  The  reaction  is  also  applicable  to  aromatic 
chlorides  which  contain  the  halogen  in  the  side-chain  : 

C6H5.CH,.C1  +  C6H6  -  C6H5.CH2.C6H5  +  HC1 

Benzyl  chloride  Diphenyl  methane 

NO2.C6H4.CH2.C1  +  C6H6=  NO2.C6H4.CH2.C6H,  +  HC1. 

Nitrodiphenyl  methane 

As  the  chlorides  of  dibasic  acids  yield  diketones,  the  alkylene  chlorides 
or  bromides,  as  well  as  tri-  and  tetra-halogen  substituted  hydrocarbons, 
can  react  with  several  hydrocarbon  molecules,  e.g.  : 

2CH+  CHBr  —  CHBr  =  CH.CH.  CH.CH   +  2  HBr 


Dibenzyl  = 
s-Diphenyl  ethane 


65 


3  C6H6  +  CHC13  =  CH  .  (C6H5)3  +  3  HC1 

Chloroform  Triphenyl  methane 


5  - 

4C6H6-|-CHBr2  —  CHBr2  =  CH    —  CH     +4  HBr. 

C6H5      C6H5 


Acetylene  tetrabromide 


s-Tetraphenyl  ethane 


In  the  latter  reaction,  anthracene  is  also  formed,  according  to  the 
equation  : 


4  HBn 


Anthracene 


For  the  synthesis  of  aromatic  acids  the  Friedel-Crafts  reaction  is  also 
of  value,  although  the  acids  themselves  are  not  directly  obtained,  but 
derivatives  of  them,  which  upon  saponification  yield  the  free  acid,  e.g. : 

C6H6  +  Cl .  CO .  NH2  -  C6H5 .  CO .  NH2  +  HC1, 

Urea  chloride  Benzamide 


AROMATIC  SERIES  325 

C6H6  +  C6H5  .  NCO    =  C6H5  .  CO  .  NH  .  C6H5 

Phenyl  cyanate  Benzanilide 

C6H6  +  C6H5.NCS    =  C6H5.CS.NH.C6H3. 

Phenyl  mustard  oil  Thiobenzanilide 

The  last  two  reactions  are  to  be  considered  as  cases  of  the  normal 
Friedel-Crafts  reaction,  since  the  cyanate  and  mustard  oil  unite  in  the 
first  phase  with  hydrochloric  acid,  forming  an  acid-chloride,  which  then 
reacts  with  the  hydrocarbon  with  elimination  of  hydrochloric  acid,  e.g.  : 

/NH.C6H5 
C6H5.NCO 


Phenyl  carbarn  ine  chloride 

If  one  considers  that  in  the  modifications,  in  place  of  the  hydro- 
carbons, ethers,  mono-  and  poly-acid  phenols,  naphthalene,  thiophene, 
diphenyl,  naphthol-ethers,  halogen  substitution  products  of  hydro- 
carbons, and  many  other  compounds  can  be  used,  the  great  value 
of  the  Friedel-Crafts  reaction  will  be  readily  understood. 

Concerning  the  role  which  aluminium  chloride  plays  in  the  reaction, 
it  is  still  not  perfectly  clear  ;  certain  it  is  that  hydrocarbons  as  well  as 
phenol-ethers  unite  with  it  to  form  double  compounds  which  are  of 
assistance  in  causing  the  reaction  to  take  place. 

(b)  By  the  action  of  hydroxylamine  on  aldehydes  and  ketones, 
oximes1  (aldoximes,  ketoximes)  are  formed  in  accordance  with  the 
following  typical  reactions  : 

C6H5  .  CHO  +  NH2  .  OH         =  C6H5  .  CH=N  .  OH  +  H2O 

Benzaldoxime 

C6H5.C.C6H5 
C6H5  .  CO  .  C6H5  +  NH2  .  OH  =  N  +  H2O. 


OH 


Benzophenone  oxime 

Oximes  may  be  obtained  by  three  methods:  (i)  The  alcoholic 
solution  of  the  aldehyde  or  ketone  may  be  treated,  generally,  with  a 
concentrated  water  solution  of  hydroxylamine  hydrochloride  and  the 
mixture  allowed  to  stand  at  the  ordinary  temperature,  or  it  may  be 
heated  in  a  flask  provided  with  a  reflux  condenser,  or  in  a  bomb-tube. 
An  addition  of  a  few  drops  of  concentrated  hydrochloric  acid  often 

18.15,1324. 


326  SPECIAL  PART 

expedites  the  reaction.  (2)  The  formation  of  oximes  may  be  brought 
about  by  the  use  of  free  hydroxylamine  obtained  by  treating  its  hydro- 
chloride  with  the  theoretical  amount  of  a  solution  of  sodium  carbonate 
(3)  Oximes  may  in  many  cases  be  very  easily  obtained,  if,  as  above* 
for  one  carbonyl  group  three  molecules  of  hydroxylamine  hydro- 
chloride  and  nine  molecules  of  potassium  hydroxide  are  used ;  in  the 
presence  of  a  large  excess  of  hydroxylamine  in  a  strongly  alkaline 
solution,  generally  a  very  smooth  decomposition  takes  place.  Since 
the  oximes  possess  a  weak  acid  character,  under  these  conditions  the 
alkali  salt  of  the  oxime  is  first  obtained,  e.g. : 

C6H5.C.C6H6 


1 


K 

from  which  the  free  oxime  is  liberated  by  treating  it  with  an  acid. 

Of  especial  significance  for  the  stereo-chemistry  of  nitrogen  are  the 
oximes  of  aldehydes  as  well  as  those  of  the  unsymmetrical  ketones. 
By  the  action  of  hydroxylamine  on  benzaldehyde,  e.g.,  there  is  formed 
not  only  a  single  oxime,  but  a  mixture  of  two  stereo-isomers.  This  is 
also  true  when  oximes  are  formed  from  many  unsymmetrical  ketones. 
The  existence  of  these  isomers  is  explained  by  the  assumption  that 
the  three  valencies  of  nitrogen  do  not  lie  in  a  plane,  but  that  they 
extend  into  space,  proceeding  from  a  point  like  the  three  edges  of  a 
regular  triangular  pyramid.1  Since,  e.g.,  in  the  formation  of  benzald- 
oxime,  the  hydroxyl-group  of  the  hydroxylamine  is  vicinal  to  either 
the  phenyl-group  or  hydrogen  atom,  the  two  following  stereo-isomers 
are  possible : 

C6H5.C.H  C6H5.C.H 

and 
HO— N  N— OH 

OH  vicinal  to  C6H5  OH  vicinal  to  H 

The  stereoisomeric  forms  of  an  unsymmetrical  ketone  are,  according  to 
this  conception,  to  be  expressed  by  the  following  formulae,  e.g. : 

BrC,H4 .  C .  C6H5  BrC6H4 .  C .  C6H5 

and 
HO— N  N— OH 

OH  vicinal  to  C6H4Br  OH  vicinal  to  C6H, 


1  B.  23,  ii,  1243. 


AROMATIC   SERIES  32? 

With  symmetrical  ketones  it  is  obviously  immaterial  upon  which  of 
the  two  similar  sides  the  hydroxyl-group  finds  itself,  so  that  here  only 
one  oxime  is  possible. 

In  this  place  the  two  mono-oximes  and  three  dioximes  of  benzil  may 
be  referred  to  again.  These  compounds  gave  the  impetus  to  the 
investigations1  of  this  class  of  compounds.  They  are  explained  by 
the  following  space-formulae : 

C(!H5 .  C .  CO .  C6H5  C6H5 .  C .  CO .  C6H5 

II  and  || 

HO— N  N— OH 

C6H5 .  C .  C .  C6H5  C6H5 .  C C .  C6H5  C6H5 .  C C .  C6H5 

II    II  ,11  II  II  II 

HO— N  N— OH  HO— N    HO— N  N— OH  HO— N 

Not  all  aldehydes  and  unsymmetrical  ketones  yield  two  oximes.  In 
many  cases  one  form  is  so  unstable  (labile)  that  only  the  other 
(stabile)  modification  exists. 

(<:)  If  phosphorus  pentachloride  is  allowed  to  act  on  an  oxime,  it 
is  transformed  into  an  anilide,2  e.g. : 

C6H5.C.CBH5 


=  C6H5.NH.CO.C6H5 

Benzanilide 

OH 

Benzophenone  oxime 


This  so-called  Beckmann  transformation  has  been  of  great  significance 
for  the  explanation  of  the  constitution  of  the  isomeric  oximes.  If,  eg., 
phosphorus  pentachloride  is  allowed  to  act  on  both  of  the  above 
formulated  stereoisomeric  oximes  of  the  brombenzophenone,  the  same 
compounds  are  not  obtained  from  both,  but  two  different  ones,  which, 
as  follows  from  their  saponification  products,  correspond  on  the  one 
hand  to  the  benzoyl  derivative  of  bromaniline,  and,  on  the  other,  to 
the  brombenzoyl  derivative  of  aniline : 

CGH5 .  CO  .  NH  .  C(;H4 .  Br  and  BrC6H4 .  CO  .  NH  .  C6H5 

The  transformation  takes  place,  probably,  in  the  following  way:  If 
phosphorus  pentachloride  is  allowed  to  act  on  an  oxime,  the  hydroxyl- 
group  is  replaced  by  chlorine  : 


i  B.  16,  503;  21,  784,  1304,  3510;  22,  537,  564,  1985,  1996. 
a  B.  19,  988 ;  20,  1507  and  2580;  A.  252,  i. 


328  SPECIAL   PART 

C6H5.C.C6H5  C6H5.C.C6H5 


N  +PC15=  N  +HC1  +  POC13 

OH  Cl 


But  a  compound  of  this  kind,  in  which  chlorine  is  united  with  nitrogen, 
is  unstable,  and  it  is  immediately  transformed  into  a  more  stable  imido- 
chloride,  the  chlorine  atom  being  replaced  by  a  phenyl-group : 

C6H5.C.C6H5  C6H5.C.C1 

i!  II 

N  — >-  N 

Cl  CCH5 

Imidochloride  of  Benzanilide 
(Compare  p.  154) 

If  this  is  now  treated  with  water,  benzanilide  is  formed,  in  accord- 
ance with  the  following  equation : 

C6H5 .  C  .  Cl  =  N  .  C6H5  +  H,O  =  C6H5 .  CO  .  NH  .  C6H5  +  HC1 

If  the  oxime  of  brombenzophenone,  formulated  above,  is  subjected 
to  a  similar  reaction,  the  unstable  chlorides  are  first  obtained: 

Br .  C6H4 .  C ,  CCH5  Br .  C6H4 .  C .  C6H5 

II  and  || 

Cl— N  N— Cl 

Cl  vicinal  to  C6H4Br  Cl  vicinal  to  C6H6 

If  the  most  probable  assumption  is  now  made,  that  the  chlorine 
atom  gives  up  its  position  to  the  vicinal  hydrocarbon  radical,  there  are 
formed : 

C1.C.C,H5  Br.C,H4.C.Cl 

I!  and  || 

Br.C6H4.N  N.C6H5 

from  which,  by  treatment  with  water,  there  are  obtained : 

Br .  C6H4 .  NH  .  CO  .  C6H5  and  Br .  C6H4 .  CO  .  NH  .  C6H5 

Benzoyl  bromanilide  Brombenzoyl  anilide 

Upon  saponification,  these  yield  : 
Br.CGH4.NH2  +  C6H5.CO.OH    and     Br.  C6H4.  CO  .  OH  +  C6H5NH2 

Bromanilme  Benzo'ic  acid  Brombenzoic  acid  Aniline 


AROMATIC  SERIES  32Q 

That  hydrocarbon  radical  which  in  the  oxime  was  vicinal  to  the 
hydroxyl-group,  is,  therefore,  on  saponification  of  the  polymerised 
product,  obtained  in  the  form  of  a  primary  amine.  In  this  way,  the 
constitution  of  the  stereoisomeric  oximes  of  the  unsymmetrical  ketones 
is  determined. 

Whatever  may  be  the  space  configuration  of  the  stereoisomeric  al- 
doximes,  the  derivatives  containing  an  acid  radical  (acetyl  derivative) 
of  the  one  form  easily  yield  an  acid-nitrile  on  being  treated  with  soda, 
while  the  second  form  does  not.  The  hypothesis  proposed,  which 
seems  very  probable,  suggests  'that  in  the  first  case  the  acid  radical  (or 
in  the  corresponding  oxime)  the  hydroxyl-group  is  vicinal  to  the  alde- 
hyde hydrogen  atom,  while  in  the  second  case  it  is  vicinal  to  the  hydro- 
carbon residue  : 


C6H5.C. 

N. 


H 
OH 


Owin     to  the  nearness  of  the     CHr.C.H.  Yields  no 


oxygen  and  hydroxyl,  it  loses  nitrile. 


water  easily,  and  yields  a  ni- 

Syn-Oxime  .    .,      r  w  r  =  fj  Anti-Oxime 


34.   REACTION:   REDUCTION  OF  A  KETONE  TO  A  HYDROCARBON 
EXAMPLE  :    Diphenyl  Methane  from  Benzophenone  l 

A  mixture  of  10  grammes  of  benzophenone,  12  grammes  of 
hydriodic  acid  (boiling-point,  127°),  and  2  grammes  of  red  phos- 
phorus is  heated  in  a  sealed  tubV'  for  6  hours  at  160°.  The 
reaction-mixture  is  then  treated  with  ether,  poured  into  a  small 
separating  funnel,  and  shaken  up  with  water  several  times.  The 
ethereal  solution  is  filtered  through  a  small  folded  filter,  and  dried, 
the  ether  evaporated,  and  the  residue  distilled.  Boiling-point, 
263°.  On  cooling,  the  diphenyl  methane  solidifies  to  crystals 
which  melt  at  -2  7°.  Yield,  almost  quantitative. 

Hydriodic  acid,  especially  at  high  temperatures,  is  an  extremely 
energetic  reducing  agent,  which  can  be  used  to  effect  reduction  when, 
as  in  the  above  case,  another  reducing  agent,  e.g.,  a  metal  and  acid, 
could  not  be  employed.  The  reducing  action  depends  on  the  following 
decomposition  : 


1  B.  7,  1624.  2  Before  opening  the  tube,  see  page  67. 


330  SPECIAL   PART 

The  above  reaction  takes  place  in  accordance  with  the  following 
equation : 

C6H5 .  CO  .  CCH5  +  4  HI    =  C6H5 .  CH2  .C6H5  +  H2O  +  2  I2 

Diphenyl  methane 

With  the  aid  of  hydriodic  acid,  not  only  ketones  but  also  aldehydes 
and  acids  may  be  reduced  to  the  hydrocarbon  from  which  they  are 
derived,  e.g. : 

C,.H5 .  CHO  +  4  HI  =  C,H5 .  CH,  +  H2O  +  4  I 

Toluene 

C6H5 .  CO  .  OH  +  6  HI      =  CCH5 .  CH3  +  2  H2O  +  3  I2 

Benzoic  acid  Toluene 

C17H35  .  CO  .  OH  +  6  HI  =  C18H38  +  2  H2O  +  3  I2 

Stearic  acid  Octodecane 

Alcohols,  iodides,  etc.,  can  also  be  reduced  to  their  final  reduction 
products,  the  hydrocarbons,  e.g.  : 

C2H5I  +  HI  =  C2H6  +  I2 

Ethyl  iodide  Ethane 

CH2.OH  CH3 

CH.OH  +6.HI  =CH2  +  3H20  +  3lf 

CH2.OH  CH3 

Glycerol  Propane 

By  heating  with  hydriodic  acid,  the  unsaturated  compounds  take  up 
hydrogen,  e.g.  : 

C6H6  +  6HI  =C6H12  +  3I2 

Hexahydrobenzene 

The  effect  of  hydriodic  acid  is  increased  by  the  addition  of  red 
phosphorus.  Under  these  conditions,  during  the  course  of  the  re- 
action, the  liberated  iodine  unites  with  the  phosphorus  to  form  phos- 
phorus tri-iodide : 

3  I  +  P  =  PI3 

which  with  the  water  present  again  decomposes  to  form  hydriodic  acid : 
PI3  +  3  H,0  =  3  HI  +  P(OH)3 

Phosphorous  acid 

A  definite  amount  of  hydriodic  acid  can  thus,  provided  a  sufficient 
quantity  of  phosphorus  is  present,  act  as  a  continuous  reducing  agent. 


AROMATIC   SERIES 


331 


35.  REACTION:  ALDEHYDE  SYNTHESIS  —  GATTERMANN-KOCH 
EXAMPLE  :  p-Tolylaldehyde  from  Toluene  and  Carbon  Monoxide 1 

To  30  grammes  of  freshly  distilled  toluene  (boiling-point  110°) 
contained  in  a  wide-necked  vessel  (an  "  extract  of  beef"  jar  is  con- 
venient) cooled  with  water,  add,  not  too  quickly,  45  grammes  of 
pulverised,  freshly  prepared  aluminium  chloride  and  5  grammes 
pure  cuprous  chloride  (see  page  389).  The  vessel  is  closed  by  a 
three-hole  cork ;  in  the  middle  hole  is  inserted  a  glass  tube  which 
carries  a  stirrer  (paddle  wheel  of  glass)  ;  the  other  holes  are  used 
for  the  inlet  and  outlet  tubes  (Fig.  75). 
After  the  apparatus  has  been  fastened  firm- 
ly in  a  clamp  it  is  immersed  into 
a  casserole  filled  with  water  at 
20°.  A  current,  not  too  rapid,  of 
carbon  monoxide  and  hydro- 
chloric acid  gas  is  led  in  through 
the  prong-shaped  tube  while  the  stirrer  is 
set  in  motion  (a  small  motor  is  convenient). 
The  carbon  monoxide,  contained  in  a  gas- 
ometer of  about  10  litres,  is  passed  first 
through  a  solution  of  caustic  potash2  ( i  :  i) 
and  then  through  a  wash-bottle  containing 
concentrated  sulphuric  acid.  The  hydro- 
chloric acid  is  generated  in  a  Kipp  ap- 
paratus from  fused  ammonium  chloride  and 
concentrated  sulphuric  acid.  It  is  passed 


FIG.  75. 


through  a  wash-bottle  containing  concentrated  sulphuric  acid. 
The  gas  currents  are  so  regulated  that  the  volume  of  the  carbon 
monoxide  is  about  twice  as  large  as  that  of  the  hydrochloric  acid. 
The  escaping  gas  is  led  directly  to  the  hood  opening.  In  the 
course  of  an  hour  when  about  1-2  litres  of  carbon  monoxide  have 
been  passed  into  the  mixture,  the  temperature  rises  to  25-30° ; 
the  remainder  of  the  gas  is  passed  in  during  four  to  five  hours. 

1  B.  30,  1622;  31,  1149.     A.  347,  347. 

2  If  carbon  monoxide  is  prepared  from  formic  acid,  the  caustic  potash  wash- 
bottle  is  unnecessary. 


332 


SPECIAL   PART 


If  the  reaction- mixture  should  become  so  viscous  before  the  lapse 
of  this  time  that  the  stirrer  revolves  only  with  difficulty,  the  re- 
action may  be  stopped.  The  viscid  product  is  then  poured  into 
a  large  flask  containing  crushed  ice ;  the  aldehyde  formed  and 
any  unattacked  toluene  is  distilled  over  with  steam.  The  distil- 
late—  oil  and  water  —  is  then  shaken  up  with  a  sodium  bisulphite 
solution  for  a  long  time.  The  toluene,  remaining  undissolved,  is 
separated  in  a  dropping  funnel.  If  the  aldehyde-bisulphite  com- 
pound should  crystallise  out,  water  is  added  until  it  dissolves.  The 
filtered  water  solution  is  then  treated  with  anhydrous  soda  until  it 
shows  a  decided  alkaline  reaction ;  the  aldehyde  is  then  again 
distilled  over  with  steam.  It  is  extracted  from  the  distillate  with 
ether.  Upon  evaporating  the  ether,  from  20-22  grammes  of  per- 
fectly pure  tolylaldehyde  remains.  Boiling-point,  204°. 

Preparation  of  Carbon  Monoxide 

i.   From  Oxalic  Acid. 

In  a  round  litre  flask  heat  100  grammes  of  crystallised  oxalic 
acid  with  600  grammes  of  concentrated  sulphuric  acid.1  The  gases 
evolved  are  passed  into  two 
large  wash-cylinders  (Fig.  74) 
filled  with  a  solution  of  caus- 
tic potash  (i  part  caustic 
potash  to  2  parts  of  water), 
and  then  into  a  gasometer 
(Fig.  76).  At  first  the  sul- 
phuric acid  is  heated  some- 
what strongly.  As  soon  as 
the  oxalic  acid  has  dissolved 
and  a  regular  current  of  gas 
comes  off,  the  flame  is 
lowered.  Before  filling  the 
gasometer  the  gas  is  tested 
by  collecting  a  test-tube 
full  over  water  and  apply- 
ing a  match.  So  long  as 
air  remains  in  the  apparatus, 
a  slight  explosion  will  occur. 
But  as  soon  as  pure  gas  is 
evolved,  it  burns  quietly  in  the  tube.  It  is  then  admitted  into  the 
gasometer.  When  the  evolution  of  gas  ceases,  the  apparatus  is  taken 

1  The  outlet  tube  through  which  the  gaseous  mixture  passes  before  coming  in 
contact  with  the  caustic  potash  solution  should  be  as  wide  as  practicable,  in  order 
that  it  may  not  be  clogged  by  the  sublimed  oxalic  acid. 


AROMATIC   SERIES  333 

apart.  Since  carbon  monoxide  is  poisonous,  the  experiment  is  carried 
out  under  the  hood,  and  care  is  taken  not  to  breathe  the  gas. 

2.   From  Formic  Acid. 

Carbon  monoxide  is  more  readily  liberated  from  formic  acid. 
The  latter  may  now  be  obtained  at  a  low  cost.  In  a  half-litre 
flask,  provided  with  a  dropping  funnel,  a  thermometer  and  an  out- 
let tube,  place  100  c.c.  (no  grammes)  of  98-100%  formic  acid. 
To  this  add,  gradually,  concentrated  sulphuric  acid.  Upon  the 
addition  of  about  50  c.c.  of  acid  the  temperature  will  rise  to  60- 
70°.  The  acid  is  now  added  more  slowly,  drop  by  drop,  in  order 
to  keep  the  temperature  at  50-60°.  If  necessary,  the  mixture  is 
gently  heated  on  a  water-bath  for  a  short  time.  When  the  air  has 
been  completely  replaced,  the  gas,  consisting  of  pure  carbon 
monoxide,  is  admitted  into  the  gasometer. 

If  it  is  desired  to  avoid  the  use  of  a  gasometer,  a  regular  and 
continuous  current  of  carbon  monoxide  may  be  generated  as 
follows :  A  litre  flask,  provided  with  a  safety-tube,  containing 
200  grammes  of  oxalic  acid  and  200  grammes  of  sulphuric  acid 
(cone.),  is  heated  in  an  oil-bath  to  120° ;  the  temperature  is 
gradually  increased  according  to  the  conditions.  If  the  gas  be 
passed  first  into  two  caustic  potash  cylinders,  and  then  into  two 
sulphuric  acid  (cone.)  cylinders,  it  may  be  used  directly  for  the 
synthesis.  Or,  the  carbon  monoxide  obtained  from  formic  acid 
may  be  used  directly,  after  it  has  been  dried  by  passing  through 
a  wash-bottle  containing  concentrated  sulphuric  acid.  But  the 
yield  of  aldehyde  is  not  as  good  as  when  a  gasometer  is  used. 

A  direct  synthesis  of  the  aromatic  aldehydes  by  means  of  the  Friedel- 
Crafts  reaction  could  not  be  brought  about  until  recently,  because  of 
the  instability  of  formyl  chloride,  which,  if  formed,  decomposes  imme- 
diately into  carbon  monoxide  and  hydrochloric  acid  : 
H  .  CO  .  Cl  =  CO  +  HC1 

If  it  were  stable,  it  should  form  aldehydes,  in  accordance  with  this 
equation  :  x  |H  +  aj .  Co  .  H  =  X  .  COH  +  HC1 

But  now  it  is  known  that  a  mixture  of  carbon  monoxide  and  hydro- 
chloric acid  in  the  presence  of  cuprous  chloride,  which  combines  with 
the  former,  behaves  like  formyl  chloride. 

The  Gattermann-Koch  synthesis  may  be  expressed  by  the  following 
equation :  CH 

C6H/  =C6H4/<H°+ 

NH  +  CII.CO.H  \COH 


From  other  hydrocarbons  like  o-  and  m-xylene,  mesitylene,  ethylben- 
zene,  diphenyl,  etc.,  in  an  analogous  way,  aldehydes  may  be  obtained. 
As  has  been  shown  in  the  ketone  syntheses,  the  acid  radical  goes  into 
the  para  position  to  the  alky]  residue,  so  also  in  the  aldehyde  syntheses 


334  SPECIAL  PART 

the  aldehyde  group  always  enters  the  para  position  to  the  alkyl  residue 
Thus  from  toluene  there  is  obtained : 


:OH 


From  o-xylene 


From  m-xylene 


Y 

COH 


Since  the  Friedel-Crafts  reaction,  when  applied  to  phenol  ethers,  yields 
the  corresponding  aldehydes  far  more  easily  than  the  same  reaction 
applied  to  the  hydrocarbons,  it  is  remarkable  that  the  Gattermann-Koch 
method  cannot  be  used  with  phenol  ethers.  If  it  be  desired  to  obtain 
aldehydes  from  them,  hydrocyanic  acid  is  used  in  place  of  carbon  mon- 
oxide ;  in  these  cases  the  presence  of  cuprous  chloride  is  unnecessary. 
The  action  takes  place,  due  to  the  union  of  hydrocyanic  and  hydro- 
chloric acids  to  form  the  chloride  of  imidoformic  acid  : 


== 
\C1 

which,  under  the  influence  of  aluminium  chloride,  reacts  with  the  phenol 
ether,  liberating  hydrochloric  acid  : 


OCH 


-  C6H4/  +  HC1 

+  ClLCH— NH  \CH=;NH 


AROMATIC   SERIES  335 

There  is  thus  obtained  first  the  aldehyde-imide  which,  through  the 
action  of  acids,  passes  over  into  the  aldehyde  with  great  ease  : 

/OCH3  /OCH3 

C6H4<  _     -  NH3  +  C6H/ 

HjO  \CHO 


In  this  way  it  is  possible  to  introduce  the  aldehyde  group  into  phenol 
ethers  as  well  as  into  the  phenols.  The  latter  always  enters  the  para 
position  to  the  oxalyl  or  hydroxyl  groups.  The  carbon  monoxide  is 
obtained  in  accordance  with  the  following  equations  : 

COOH 

(1)  |  =CO  +  CO2+  H.O 
COOH 

The  mixture  of  gases  is  separated  by  passing  it  through  a  solution  of 
caustic  soda  or  caustic  potash  ;  the  carbon  dioxide  is  absorbed,  and  the 
carbon  monoxide  emerges  in  a  pure  condition. 

(2)  H  .  COOH  =  CO  -f  H2O 

36.  REACTION:   SAPONIFICATION  OF  AN  ACID-NITRILE 
EXAMPLE  :  Toluic  Acid  from  Tolyl  Nitrile  l 

The  p-tolyl  nitrile  obtained  in  Reaction  10  is  heated  with 
slightly  diluted  sulphuric  acid  on  the  sand-bath  in  a  round  flask 
with  reflux  condenser  until  crystals  of  toluic  acid  appear  in  the 
condenser.  For  each  gramme  of  the  nitrile  a  mixture  of  6 
grammes  of  concentrated  sulphuric  acid  with  2  grammes  of  water 
is  used.  After  cooling  it  is  diluted  with  water,  the  acid  separating 
out  is  filtered  off  and  washed  several  times  with  water.  A  small 
portion  is  dissolved  in  a  little  alcohol,  and  hot  water  added  until 
the  solution  just  becomes  turbid  ;  it  is  then  boiled  jome  time 
with  animal  charcoal.  On  cooling,  the  pure  acid  is  obtained. 
Melting-point,  177°.  Yield,  80-90%  of  the  theory. 

By  saponification  in  a  narrow  sense  is  understood  the  splitting  up 
of  an  acid-ester  into  an  alcohol  and  acid.  It  is,  however,  used  in  a 
wider  sense  to  indicate  the  conversion  of  acid-derivatives,  like  nitriles, 
amides,  substituted  amides,  e.g.,  anilides,  into  acids  of  the  same  name. 
Saponification  may  be  conducted  either  in  an  alkaline  or  an  acid  solu- 
tion. Thus,  for  instance,  acetamide  reacts  on  heating  with  a  solution 

1  A.  258,  10. 


SPECIAL   PART 

of  caustic  potash  or  caustic  soda  with  the  formation  of  the  alkali  salt 
of  acetic  acid  and  the  evolution  of  ammonia.  Nitriles  and  esters  may 
frequently  be  saponified  by  water  solutions  of  the  alkalies.  Further, 
alcoholic  caustic  potash  or  caustic  soda  can  be  used  for  a  similar  pur- 
pose. Finally,  saponification  may  be  effected  by  heating  with  a  sodium 
carbonate  solution  under  pressure ;  this  method  is  especially  well 
adapted  for  difficultly  saponifiable  amides  or  anilides. 

In  order  to  effect  saponification  in  acid  solution,  the  substance  to  be 
saponified  is  heated  with  either  hydrochloric  acid  or  sulphuric  acid  in 
varying  degrees  of  dilution,  e.g. : 

/CH3  /CH3 

C6H/          +  2  H20  =  CeH/  +  NH3 

\CN  \CO.OH 

p-Tolyl  nitrile  p-Toluic  acid 

Acid  amides  may  be  easily  saponified  by  dissolving  in  concentrated 
sulphuric  acid,  cooling,  adding  sodium  nitrite,  and  then  gradually 
heating,1  e.g.  : 

C6H<5 .  CO .  N  H2  +  NOOH  =  C6H5 .  COOH  +  N2  +  H2O 

In  order  to  saponify  a  nitrile  by  this  method  it  is  first  converted  by 
heating  with  85  %  sulphuric  acid  into  the  amide,  and  this  is  treated  as 
directed  above. 

Frequently  it  is  better  to  allow  the  nitrite  to  act  directly  on  the  warm 
dilute  sulphuric  acid  solution  of  the  amide. 

The  decomposition  of  the  ethers  of  phenols  is  also  designated  as 

saponification.     Such  decomposition  cannot  be  effected  by  the  methods 

hitherto  given.     Hydriodic  acid   is   used   which,  when   heated   with 

phenol-ethers,  decomposes  them  into  the  phenol  and  the  alkyl  iodide : 

C6H5.OCH3  +  HI  =  CCH5.OH  +  CH3I 

Anisol 

Anhydrous  aluminium  chloride  may  be  used  here  with  great  advantage ; 
upon  heating,  it  acts  on  the  phenol-ether  in  the  manner  indicated  by 
the  following  equation: 

3  C6H5. OCH3  +  A1C13  =  (C6H, .  O)3A1  +  3  CH3C1 

Aluminium  salt 
of  phenol 

If  a  phenol  salt  is  treated  with  an  acid,  the  free  phenol  will  separate 
out.  This  method  presents  the  advantage  that  it  may  be  applied  to 
substances  containing,  in  addition  to  the  phenol-ether  radical,  a  redu- 
cible carbonyl  group,  which,  if  treated  with  hydriodic  acid,  would  be 
changed. 

1  B.  26,  Ref.  773;  28,  Ref.  917;  32,  1118. 


AROMATIC  SERIES  337 

37.  REACTION:  OXIDATION  OF  THE  SIDE-CHAIN  OP  AN 
AROMATIC  COMPOUND 

EXAMPLE  :  Terephthalic  Acid  from  p-Toluic  Acid 

Dissolve  5  grammes  of  the  crude  toluic  acid  obtained  in  Reac- 
tion 36  in  a  solution  of  3  grammes  of  sodium  hydroxide  in  250  c.c. 
of  water  ;  heat  in  a  porcelain  dish  on  the  water-bath,  and  gradually 
treat  with  a  solution  of  12  grammes  of  finely  powdered  potassium 
permanganate  in  250  c.c.  of  water  until,  after  long  boiling,  the  red 
colour  of  the  permanganate  no  longer  vanishes.  Alcohol  is  then 
added  until  the  liquid  is  colourless,  and,  after  cooling,  the  manga- 
nese dioxide  separating  out  is  filtered  off;  this  is  washed  with  hot 
water,  and  the  filtrate,  heated  to  boiling,  is  acidified  with  concen- 
trated hydrochloric  acid.  After  cooling,  the  terephthalic  acid  is 
filtered  off,  washed  with  water,  and  dried  on  the  water-bath.  Yield, 
90  %  of  the  theory.  Terephthalic  acid  is  insoluble  in  water.  On 
heating,  it  sublimes'  without  melting. 

It  is  a  common  property  of  aliphatic  side-chains,  united  with  the 
benzene  nucleus,  to  pass  over  to  carboxyl  groups  on  oxidation.  A 
methyl  group  requires  3  atoms  of  oxygen  for  oxidation  : 

C6H5.CH3  +  30  =  C6H5.CO.OH  +  H2O 

Toluene  Benzo'ic  acid 

If  several  side-chains  are  present  in  a  compound,  either  all  or  a  portion 
of  them  may  be  converted  into  carboxyl  groups  : 


/CH« 
C6H/ 

\CO. 


CH 


OH 
.OH 
.OH 

3 


CTT  /  r^tj 
6*13\r~'-'*13 

\CO.OH 
/ 

/CH3 
C6H^CH3  gives 

\CH3  \ 

^.OH 


C6H.£-CO .  OH 
\CO .  OH 


338  SPECIAL  PART 

If  a  side-chain  contains  s.everal  carbon  atoms,  in  many  cases  only 
the  methyl  group  at  the  end  of  the  chain  can  be  oxidised,  e.g. : 

X  .  CH2 .  CH3  +  3  O  =  X  .  CH2 .  CO .  OH  +  H2O 

But  by  an  energetic  oxidation  all  the  carbon  atoms,  with  the  excep- 
tion of  the  last,  are  split  off,  e.g. : 

C6H5 .  CH2 .  CH3  +  3  O2  =  C6H5 .  CO  .  OH  +  CO.  +  2  H2O 

Ethyl  benzene 

The  basicity  of  the  acid  derived  from  the  oxidation  of  a  hydrocarbon 
accordingly  gives  an  indication  concerning  the  number  of  side-chains 
of  the  hydrocarbon.  Derivatives  of  hydrocarbons  are  also  capable  of 
similar  reaction,  e.g. : 

'CO.  OH 

+  H2O 


Chlortoluene  Chlorbenzoic  acid 

/CH,  /CO.  OH 

C6H/          +30  =  C6H  4<  +  H20 

\NO2  \NO2 

Nitrotoluene  Nitrobenzoi'c  acid 

CH3 .  CO  .  C6H5  +  30  =  C6H5 .  CO  .  COOH  4-  H2O 

Acetophenone  Phenyl  glyoxylic  acid 

The  reaction  carried  out  above  takes  place  in  accordance  with  this 
equation  : 

/CH3  /CO.  OH 

C6H4<  +30-  C6H/  +  H20 

NCO.OH  \CO.OH 

Amines  and  phenols  cannot  be  directly  oxidised  in  most  cases,  but 
an  indirect  method  must  be  employed,  by  which  the  former  are  con- 
verted into  an  acid  derivative,  and  the  latter  into  an  ester.  If,  e.g.,  it  is 
desired  to  convert  p-toluidine  into  p-amidobenzoic  acid,  the  base  is  first 
acetylated,  and  the  acetatoluide  is  then  oxidised : 

/CH3  /CO .  OH 

C6H4<;  +3O  =  C6H4<  +  H2O 

\NH  .  CO .  CH3  \NH  .  CO .  CH3 

The  acid  thus  obtained  is  then  saponified,  and  the  desired  amida 
ben  zoic  acid  is  formed  : 

/CO.  OH  /NH0 

C6H4<  +H2O  =  C6H4<  +  CH3.CO.OH 

\NH.CO.CH,  \CO.OH 


AROMATIC   SERIES  339 

If  it  is  desired,  on  the  other  hand,  to  oxidise  a  phenol,  e.g.,  cresol, 

C6H4<^         ,  the  sulphuric  acid-  or  phosphoric  acid-ester  of  it  is  first 

\OH 

prepared  and  oxidised ;  the  reaction-product  is  then  saponified.  As 
oxidising  agent,  dilute  nitric  acid  (i  vol.  cone,  nitric  acid  to  3  vol. 
water1),  chromic  acid  or  potassium  permanganate  is  used.  The  mildest 
effect  is  obtained  with  the  nitric  acid,  which  is  therefore  used  when  all 
the  side-chains  are  not  to  be  oxidised,  but  only  a  portion  of  them,  e.g.: 

/CH3  /CHo 

C«H/  >-       CCH/ 

\CH3  \CO.OH 

Nitric  acid  is  also  used  in  other  cases,  where,  as  frequently  happens 
with  ortho  derivatives,  other  oxidising  agents  totally  destroy  the  sub- 
stance. 

Chromic  acid,  in  the  form  of  its  anhydride  generally,  dissolved  in 
glacial  acetic  acid,  or  as  a  water  solution  of  potassium  dichromate  or 
sodium  dichromate  acidified  with  dilute  sulphuric  acid,  can  also  be 
used  as  an  oxidising  agent,  not  only  in  the  case  in  hand,  but  also  for 
the  oxidation  of  alcohols,  ketones,  etc.  In  oxidation  reactions,  two 
molecules  of  chromic  anhydride  (CrO3)  give  three  atoms  of  oxygen : 

2  CrO3  =  C2O3  +  30 

For  the  oxidation  of  aromatic  hydrocarbons,2  experience  has  shown 
that  a  good  oxidising  mixture  is  40  parts  of  potassium  dichromate, 
55  parts  of  concentrated  sulphuric  acid,  diluted  with  twice  its  volume 
of  water. 

With  potassium  permanganate3  oxidation  can  be  effected  either  in 
alkaline  or  in  acid  solution.  In  the  first  case,  manganese  dioxide  is 
deposited : 

2  KMnO4  +  H,O  =  3  O  +  2  MnO2  +  2  KOH 

Two  molecules  of  potassium  permanganate  yield,  therefore,  in  alkaline 
solution,  three  atoms  of  oxygen. 

In  acid  solution  (sulphuric  acid),  no  manganese  dioxide  separates 
out,  since  it  is  dissolved  by  the  sulphuric  acid,  with  evolution  of 
oxygen,  to  form  manganous  sulphate : 

2  KMnO4  +  3  H2SO4  =  50  +  K2SO4  +  2  MnSO4  +  3  H2O 

Two  molecules  of  the  permanganate  in  acid  solution,  therefore,  yield 
5  atoms  of  available  oxygen. 

In  oxidising  with  potassium  permanganate,  a  2-5  %  solution  is  gen- 
erally used.  An  excess  of  the  permanganate  can  be  removed  by  the 
addition  of  alcohol  or  sulphurous  acid.  The  alcohol  is  oxidised  into 
aldehyde  or  acetic  acid,  and  the  sulphurous  acid  into  sulphuric  acid. 

i  A.  137,  302.  2  A.  133,  41.  s  B.  7(  I057. 


340  SPECIAL  PART 


38.  REACTION :  SYNTHESIS  OF  OXY ALDEHYDES.  REIMER  AND 

TIEMANNi 

EXAMPLE  :  Salicylic  Aldehyde  from  Phenol  and  Chloroform 

In  a  round  litre  flask  dissolve  80  grammes  of  caustic  soda 
in  80  c.c.  of  water  by  heating.  Add  25  grammes  of  phenol ; 
cool  the  solution  without  shaking  to  60-65°  by  immersion  in  cold 
water.  By  means  of  a  two-hole  cork  attach  to  the  flask  an  effective 
reflux  condenser,  arid  insert  a  thermometer  the  bulb  of  which  dips 
into  the  liquid.  Add  60  grammes  of  chloroform  gradually,  as  fol- 
lows :  At  first  add  one-third  through  the  condenser ;  on  gentle 
shaking  the  liquid  becomes  a  fuchsine-red  in  colour.  After  a 
short  time  the  colour  changes  to  orange,  and  the  temperature 
rises.  When  it  reaches  70°  the  entire  flask  is  immersed  in  cold 
wafer  until  the  thermometer  indicates  65°.  In  this  way  during 
the  entire  reaction  the  temperature  is  always  kept  between  65° 
and  70°.  Should  it  fall  below  60°,  the  mixture  is  warmed  by  im- 
mersing it  a  short  time  in  hot  water  until  the  mercury  rises  to  65°. 
After  10-15  minutes  the  second  third  of  the  chloroform  is  added, 
observing  the  precautions  just  given.  Finally,  after  about  20 
minutes,  the  remainder  of  the  chloroform  is  added.  Since  toward 
the  end  the  reaction  takes  place  very  quietly,  the  flask  is  frequently 
immersed  in  hot  water  in  order  to  maintain  the  temperature 
between  the  prescribed  limits.  The  synthesis  requires  in  all  from 
i^  to  2  hours.  Frequent  shaking  of  the  mixture,  especially  during 
the  last  phase,  increases  the  yield  materially.  When  the  reaction 
is  complete  the  chloroform  is  distilled  off  with  steam.  The  orange* 
coloured  alkaline  liquid  is  allowed  to  cool  somewhat,  and  is  acidi- 
fied carefully  with  dilute  sulphuric  acid,  upon  which  it  becomes 
almost  colourless ;  finally,  steam  is  passed  into  it  until  drops  of  oil 
no  longer  go  over. 

The  distillate  is  then  extracted  with  ether,  the  ethereal  solution 
separated  from  the  water,  and  the  ether  evaporated.  The  residue, 
consisting  of  unchanged  phenol  and  salicylic  aldehyde,  is  treated 

1  B.  9,  423,  824 ;  10,  1562 ;  15,  2685,  etc. 


AROMATIC   SERIES  341 

with  twice  its  volume  of  a  concentrated  solution  of  commercial 
sodium  bisulphite.  Upon  stirring  well  for  a  long  time  with-a  glass 
rod,  a  solid  paste  of  the  double  compound  of  the  aldehyde  and 
bisulphite  should  separate  out.  After  standing  from  ^-i  hour  the 
crystals  are  filtered  with  suction,  pressed  firmly  together,  and 
washed  several  times  with  alcohol  to  remove  completely  the  ad- 
hering phenol,  and  finally  with  ether.  The  pearly,  lustrous  leaflets 
are  then  well  pressed  out  on  a  porous  plate  and  the  aldehyde  set 
free  by  a  gentle  warming  with  dilute  sulphuric  acid  on  the  water- 
bath.  On  cooling,  the  mixture  is  extracted  with  ether,  the  ethereal 
solution  dried  over  anhydrous  Glauber's  salt,  the  ether  is  evapo- 
rated, and  the  residue  of  the  pure  aldehyde  is  distilled.  Boiling- 
point,  196°.  Yield,  10-12  grammes. 

The  small  amount  of  the  p-oxybenzaldehyde  formed  with  the 
salicylic  aldehyde  is  not  volatile  with  steam,  and  remains  back  in 
the  flask  after  the  distillation  with  steam.  In  order  to  obtain  it, 
the  residue  remaining  in  the  flask  after  cooling  is  filtered  through 
a  folded  filter,  and  the  clear  filtrate  saturated  with  solid  salt,  upon 
which  the  p-oxybenzaldehyde  separates  out  at  once  or  on  stand- 
ing. If  this  be  filtered  off,  and  the  filtrate  extracted  with  ether, 
a  further  quantity  is  obtained,  which,  together  with  the  first,  is 
purified  by  recrystallisation  from  water  with  the  addition  of  a 
solution  of  sulphur  dioxide.  Melting-point,  116°.  Yield,  2-3 
grammes. 

The  synthesis  takes  place  in  accordance  with  this  equation : 

/ONa 

C,H5ONa  +  CHCL  +  3  NaOH  =  C,H4<  +  3  NaCl  +  2  H0O 

XCHO 

Probably  the  reaction  takes  place  in  the  two  phases : 


342  SPECIAL  PART 

By  this  method  the  aldehyde  group  may  be  introduced  into  mono- 
and  poly-acid  phenols;  it  enters  the  ortho  and  para  positions  to  a 
hydroxyl  group  : 

Phenol  gives  o-  and  p-oxybenzaldehyde, 

CH  CH3 


o-Cresol   _»  I  and 


CH,  CH 

OHG/N 

m-Cresol  *-  \___       and 

:HO 

CH3 

p-Cresol   ^  [        I  only- 

OH 
OH 

Pyrocatechin— >-          (    JO1      =  Protocatechuic  aldehyde. 

CHO 
OH  OH 


^^Isoadialdehyde  |         | 

CHO  CHO 

OH 

Hydroquinone >•    \        \  Gentisin  aldehyde. 

OH 

The  reaction  also  takes  place  with  the  ethers  of  poly-acid  phenolu 
Thus  guaiacol  gives : 

OH  OH 

OHC/NOCH,     and  O™3    Vanillin. 

V 


AROMATIC   SERIES  343 

From  resorcinmonomethyl  ether  there  are  formed  two  monoaldehydes 
and  two  dialdehydes.  The  reaction  is  also  applicable  to  oxyaldehydes 
as  well  as  oxycarbonic  acids.  Thus  from  salicylic  aldehyde  there  is 
formed  a  mixture  of  two  oxyisophthalic  aldehydes  : 

OH 
/OH  /\ 

CgHgy— CHO  p-oxybenzaldehyde  gives  :    f 

X:HO  \s 

CHO 

That  resorcin,  in  addition  to  a  monoaldehyde,  yields  a  dialdehyde, 
has  already  been  mentioned.  From  the  three  oxybenzoic  acids  are 
formed  two  oxyaldehyde  acids, 


/OH 


This  synthesis  is  capable  of  very  wide  application.  But  it  has  some 
defects.  Thus  the  yield  of  aldehyde  obtained  in  accordance  with  the 
original  directions  leaves  much  to  be  desired.  The  yield  is  very  much 
decreased  by  the  fact  that  a  portion  of  the  phenol  does  not  enter  into 
the  reaction,  and  another  portion  reacts  with  the  chloroform  to  produce 
an  ester  of  ortho  formic  acid  : 

3  C(;H5ONa  +  CHC13  =  3  Nad  +  CH(OC6H5)3 

A  portion  of  the  aldehyde  first  formed  is  lost  by  condensation  with 
some  unattacked  phenol,  forming  a  derivative  of  triphenylmethane  : 

C6H4.OH 
C/C8H4.OH 
%C6H4.OH 

XH 

Further,  a  portion  of  the  oxyaldehydes  is  converted  into  resins  by 
the  alkali. 

And  again,  many  phenols  react  as  keto-compounds,  and  give  rise  to 
varying  quantities  of  by-products,  e.g.  : 

H3C\    y|H4-Cl|CHCl2      H3C\   /CHC12 

I)  +  HC1 


Y 


p-cresol  Dichlormethyl 

[Ketodihydrotoluene]  Ketodihydrotoluene 


344 


SPECIAL   PART 


In  some  cases,  the  chief  product  of  the  reaction  consists  of  chlorinated 
ketones  of  this  order.  (B.  35,  4209  ;  A.  352,  288.) 

In  addition,  the  separation  of  the  mixture  of  the  mono-  and  dialde- 
hydes  is  often  attended  with  serious  difficulty. 

As  already  mentioned  on  page  334,  the  aldehyde  group  may  be  in- 
troduced into  phenols  by  the  use  of  condensation  agents  like  aluminium 
chloride,  zinc  chloride,  hydrocyanic  and  hydrochloric  acids.  These  re- 
actions possess  many  advantages  over  those  discussed  above.  They 
take  place  more  smoothly,  yield  only  the  p-oxyaldehydes,  and  introduce 
only  one  aldehyde  group ;  further,  only  small  amounts  of  resins  are 
formed,  and  finally  they  may  be  applied  to  phenols  like  pyrogallol, 
phloroglucin,  the  two  naphthols,  poly-acid  phenols  of  naphthalene,  etc. 
With  these  substances  the  other  reaction  is  useless.  (See  B.  31,  1765  ; 
32,  278,  etc. ;  A.  357,313-) 


39.   REACTION:  KOLBE'S   SYNTHESIS  OF   OXYACIDS 


EXAMPLE  :  Salicylic  Acid  from  Sodium  Phenolate  and 
Carbon  Dioxide1 

Dissolve  12^-  grammes  of  chemically  pure  sodium  hydroxide  in 
20  c.c.  of  water  in  a  porcelain  dish,  or  better  a  nickel  dish,  and 

with  stirring,  treat  gradually 
with  30  grammes  of  crystal- 
lised phenol.  The  greatest 
portion  of  the  water  is  then 
evaporated  by  heating  over 
a  free  flame,  the  mass  being 
continually  stirred.  As 
soon  as  a  crystalline  film 
forms  on  the  surface  of  the 
liquid,  the  heating  is  con- 
tinued with  a  luminous 
flame,  which  is  not  placed 
directly  under  the  dish,  but 
is  kept  in  constant  motion. 
In  order  to  fasten  the  dish, 
a  pair  of  crucible  tongs  is 
FlG>  77>  clamped  in  a  vertical  posi- 

tion, and  the  dish  supported  between  its  jaws.  There  is  first  ob- 
tained a  caked,  bright-coloured  mass,  which  is  crushed  from  time 
to  time  with  a  mortar-pestle.  As  soon  as  the  particles  no  longer 


ij.pr.  [2]  10,89;  27,39:  3I.397- 


AROMATIC   SERIES  345 

bake  together,  the  mass  is  pulverised  quickly  in  a  dry  mortar,  the 
dry  mass  is  then  heated  with  thorough  stirring  in  a  nickel  dish  to 
dusty  dryness.  It  is  then  placed  in  a  tubulated  retort  of  200  c.c. 
capacity.  The  retort  is  then  immersed  as  far  as  possible  in  an  oil- 
bath  (Fig.  77).  This  is  heated  to  110°,  and  at  this  temperature 
a  current  of  dry  carbon  dioxide  is  passed  over  the  sodium  pheno- 
late  (the  end  of  the  delivery  tube  is  i  cm.  above  the  upper  surface 
of  the  sodium  phenolate)  ;  this  is  passed  into  the  retort  for  an 
hour.  The  temperature  is  then  gradually  raised  (20°  per  hour) 
during  the  course  of  four  hours,  while  a  not  too  rapid  current  is 
passed  in,  to  190°.  The  mixture  is  finally  heated  1-2  hours  at 
200°.  During  the  operation  the  mass  is  stirred  several  times  with 
a  glass  rod.  After  cooling,  the  phenol  in  the  neck  of  the  retort  is 
melted  by  the  application  of  a  flame  to  the  outside,  the  dusty,  fine 
powder  is  poured  into  a  large  beaker,  the  retort  is  washed  out 
several  times  with  water,  and  the  salicylic  acid  precipitated  with 
much  concentrated  hydrochloric  acid.  After  the  reaction-mixture 
has  been  cooled  with  ice-water  a  long  time,  and  the  sides  of  the 
vessel  rubbed  with  a  glass  rod,  the  crude  salicylic  acid  is  filtered 
off,  washed  with  a  little  water,  and  pressed  out  on  a  porous  plate. 

The  purification  of  the  crude  salicylic  acid  is  accomplished 
best  with  superheated  steam.  For  this  purpose  the  acid,  in  a  dry 
condition,  is  placed  in  a  short-necked  flask,  and  heated  in  an  oil- 
bath  to  170°,  a  not  too  rapid  current  of  steam  at  a  temperature 
of  170-180°  (see  page  41)  is  passed  over  it.  The  connection 
between  the  flask  and  steam  generator  must  not  be  made  until 
the  oil-bath  and  the  steam  have  the  same  temperature.  Since  the 
acid  distilling  over  very  soon  stops  up  a  condenser  tube  of  the 
usual  width,  one  should  use  for  this  experiment  a  tube  of  2.5  cm. 
width  (width  of  mantel  5  cm.,  length  of  same  75  cm.).  The 
connecting  tube  between  the  flask  and  condenser  must  be  2  cm. 
wide,  and  as  short  as  possible.  If  the  acid  removed  from  the 
condenser  be  dissolved  in  the  watery  distillate  in  the  receiver  by 
heating,  long  colourless  needles  separate  out  on  cooling.  Melting- 
point,  156°.  Yield,  5-10  grammes. 

The  preparation  of  salicylic  acid  does  not  always  take  place 


34-6  SPECIAL   PART 

successfully  the  first  time.  The  success  of  the  experiment  depends 
particularly  on  the  conditon  of  the  sodium  phenolate,  which  must 
be  perfectly  dry}  If  it  "  cakes  "  on  heating  the  retort,  there  is 
great  probability  that  the  experiment  will  be  unsuccessful. 

The  operation  should  be  so  arranged  that  the  sodium  phenolate 
is  prepared  toward  evening,  so  that  it  may  be  allowed  to  stand  in 
a  sulphuric  acid  desiccator  over  night.  The  drying  in  the  current 
of  carbon  dioxide  is  begun  immediately  next  morning. 

The  synthesis  is  named  after  its  discoverer,  Kolbe.  It  takes  place 
in  three  phases.  In  the  first,  the  carbon  dioxide  is  added  to  the 
sodium  phenolate,  which  forms  sodium  phenyl  carbonate : 

(I .)    C6H, .  ONa  +  C02  =  C0H5 . 0 .  CO_9Na 

In  the  above  experiment  this  reaction  is  completed  during  the  heat- 
ing up  to  110°  for  one  hour.  In  the  second  phase,  the  sodium  phenyl 
carbonate  is  transformed  into  the  so-called  neutral  sodium  salicylate : 

/OH 
(II.)    C<,H..O.CO.,Na  =  C(.H4< 

xCO,Na 

while  in  the  last  phase  a  molecule  of  this  salt  reacts  with  a  molecule  of 
unchanged  sodium  phenolate  in  the  following  way : 

/OH  /ONa 

(III.)    C6H/  +  C6Ha.ONa  =  CcH/  +C6H5.OH 

XCO . ONa  XCO . ONa 

These  two  latter  reactions  take  place  during  the  gradual  heating  up 
to  200°.  Only  one-half  of  the  phenol,  therefore,  is  converted  into 
salicylic  acid,  the  second  half  being  obtained  unchanged. 

A  modification  of  the  Kolbe  synthesis  which  permits  the  immediate 
conversion  of  all  the  phenol  into  salicylic  acid  is  known  as  Schmitfs 
synthesis.  According  to  this  method,  as  in  the  other,  the  sodium 
phenyl  carbonate  is  first  prepared ;  this  is  then  further  heated  in  an 


1  The  experiment  is  more  certain  of  success  if  the  sodium  phenolate  is  heated 
a  half  hour  in  a  current  of  dry  hydrogen  at  140°  (retort  in  the  oil-bath)  before  the 
introduction  of  the  carbon  dioxide;  the  mass  must  be  cooled  to  110°  before  the 
latter  is  led  in. 


AROMATIC   SERIES  347 

autoclave  under  pressure  to  140°,  upon  which  it  is  completely  trans- 
formed into  sodium  salicylate  according  to  Equation  II.  Instead  of 
preparing  the  sodium  phenyl  carbonate  with  gaseous  carbon  dioxide, 
the  sodium  phenolate  may  be  mixed  directly  with  liquid  or  solid  carbon 
dioxide  in  the  autoclave. 

The  Kolbe  synthesis  is  capable  of  very  common  application,  since 
from  each  mon-acid  phenol,  a  carbonic  acid  may  be  obtained  in  the 
same  way  as  that  used  above.  The  carboxyl  group  under  these  condi- 
tions primarily  seeks  the  ortho  position  to  the  hydroxyl  group.  The 
derivatives  of  phenols,  e.g.  the  three  chlorphenols,  yield  chlorinated 
salicylic  acids.  With  acid-ethers  of  poly-acid  phenols  which  still  con- 


tain  a  free  hydroxyl  group,  as,  e.g.,  guaiacol,  C6H4  ,  this  reaction 

X)H 
likewise  takes  place.     From  the  two  naphthols  C10H7.OH  the  oxy- 

X)H 

naphthoic  acids  C]nHr<f  ,  can  be  obtained.  . 

XTO.OH 

If  in  the  Kolbe  reaction  instead  of  sodium  phenolate,  potassium 
phenolate  is  used,  the  para-oxybenzoiic  acid  is  obtained,  and  not  the 
ortho-acid.  The  potassium  phenolate,  like  the  sodium  phenolate,  first 
absorbs  carbon  dioxide,  and  the  potassium  phenyl  carbonate  thus 
formed,  heated  in  carbon  dioxide  up  to  1  50°,  also  yields  salicylic  acid  ; 
but  if  the  temperature  is  increased,  an  increasingly  larger  quantity  of 
the  para-acid  is  obtained,  until  finally  at  220°  the  potassium  para- 
oxybenzoate  is  the  only  product. 

The  addition  of  carbon  dioxide  is  effected  with  greater  ease  in  poly- 
acid  phenols.  With  these  compounds  the  reaction  begins  if  the  phenol 
is  boiled  in  a  water-solution  of  ammonium  carbonate  or  potassium 
hydrogen  carbonate,  e.g.  : 

/OH  /OH 

C6H/        4  HO  .  CO  .  OK  -  C6H3^-OH        +  H2O 
•X>H  \CO.OK 

Salicylic  acid  is  prepared  technically  on  the  large  scale.  Since  it 
is  an  excellent  antiseptic,  it  finds  extensive  application  in  .  preventing 
fermentation,  for  the  preservation  of  meat,  for  the  disinfection  of 
wounds.  It  may  easily  be  recognised,  since  its  water  solution  gives 
a  violet  colour  with  ferric  chloride  ;  in  this  action  it  differs  from  the 
para-  and  meta-modifications.  It  is  volatile  with  steam  ;  for  this  rea- 
son it  must  not  be  boiled  too  long  in  an  open  vessel  when  it  is  to  be 
recrystallised.  All  ortho-oxycarbonic  acids  show  this  property;  the 


348  SPECIAL  PART 

meta-  and  para-isomers  are  not  volatile  with  steam.     If  salicylic  acid 
is  heated  strongly,  it  decomposes  into  carbon  dioxide  and  phenol : 

/CO .  OH 

C6H4<  =  C6H5.OH  +  C02. 

\OH 

The  para-oxycarbonic  acids  show  the  same  property  while  the  meta- 
acids  are  stable. 

40.   REACTION:   GRIGNARD'S  REACTION 

(a)  Benzoic  Acid  from  lodobenzene.     (b)  Benzhydrol  from  lodo- 
or  Brombenzene  and  Benzaldehyde 

(a)  2.4  grammes  of  magnesium  shavings  (or  thin  magnesium 
ribbon,  about  2  mm.  in  width,  rubbed  with  fine  emery-cloth, 
cleaned  with  filter  paper,  and  cut  in  pieces  1-2  cm.  long)  are 
placed  in  a  flask  provided  with  a  reflux  condenser,  and  treated 
with  a  mixture  of  20.4  grammes  of  thoroughly  dried  iodobenzene, 
40  c.c.  of  absolute  ether l  and  a  granule  of  iodine.  The  flask  is 
dipped  in  hot  water,  or  heated  in  a  water-bath  at  the  boiling 
point  of  the  ether.  In  \—^  hour  a  white,  flocculent  precipitate 
will  begin  to  form,  and  the  heat  of  the  reaction  will  cause  the 
ether  to  boil  actively  when  the  water-bath  is  removed.  If,  now, 
the  bottom  of  the  flask  is  wrapped  up  in  dry  cloth,  so  as  to  utilise 
the  heat  of  the  reaction,  the  greater  part  of  the  magnesium  will  go 
into  solution  in  the  course  of  two  hours.  At  the  end  of  this  period 

1  For  experiments  (a)  and  (b)  absolute  ether  is  prepared  as  follows  :  250  c.c.  of 
commercial  ether  are  shaken  several  times  with  100  c.c.  of  water,  and  allowed  to 
remain  over  granular  calcium  chloride  over  night.  The  ether  is  separated  from 
the  calcium  chloride  and  treated  with  thin,  bright  scales  of  sodium.  The  vessel  is 
stoppered  with  a  cork  to  which  is  attached  a  calcium  chloride  tube,  open  at  both 
ends.  As  soon  as  the  evolution  of  gas  ceases,  the  ether  is  distilled  off  from  the 
sodium  in  the  same  vessel.  It  is  collected  in  a  suction  flask  attached  to  the  lower 
end  of  the  condenser  with  a  cork,  and  having  a  calcium  chloride  tube  connected  to 
its  side  tube  to  prevent  moisture  from  entering  the  receiver.  For  the  success  of  the 
experiments  the  use  of  thoroughly  dry  materials  and  vessels  is  absolutely  necessary. 
Should  the  progress  of  the  experiment  (the  dissolving  of  magnesium)  require  more 
time  than  is  prescribed  above,  then  the  reagents  were  not  dry  enough.  The  experi- 
ment is  repeated.  The  ether  must  again  be  kept  in  contact  with  sodium  over  night, 
and  must  be  freshly  distilled  from  the  sodium  just  before  it  is  to  be  used' 


AROMATIC   SERIES  349 

the  boiling  of  the  ether  will  either  slacken  or  entirely  cease.  It  is 
once  more  heated  for  half  an  hour  on  a  water-bath,  then  cooled  by 
surrounding  the  flask  with  ice  water.  The  condenser  is  removed, 
and  in  the  course  of  2-3  hours  a  slow  current  of  carbon  dioxide 
(dried  by  passing  through  two  wash-bottles  containing  concentrated 
sulphuric  acid)  is  run  into  the  ethereal  solution  of  phenyl  magne- 
sium iodide,  which  may  still  contain  a  small  quantity  of  undis- 
solved  magnesium.  The  flask  is  kept  cold  during  this  operation. 
The  reaction  mixture  consists  of  two  layers,  a  light  upper  layer  of 
ether,  and  a  heavy,  viscous  layer  of  the  reaction  product.  When 
too  rapid  a  current  of  carbon  dioxide  is  passed,  a  single  layer  of 
viscous  mass  will  be  obtained.  This  will  not  impair  the  success  of 
the  experiment  if  the  mixture  was  cooled  thoroughly.  It  is  now 
treated  with  finely  broken  ice,  and  with  a  cooled  mixture  of  15  c.c. 
of  concentrated  hydrochloric  acid  and  an  equal  volume  of  water. 
The  benzoic  acid  is  extracted  with  commercial  ether.  The  ether 
is  evaporated,  and  the  residue  is  gently  warmed  with  caustic 
soda  or  caustic  potash.  After  filtering  the  undissolved  portion,1 
the  alkaline  solution  is  treated  with  hydrochloric  acid.  The  pre- 
cipitated benzoic  acid  is  filtered.  More  acid  is  obtained  by 
extracting  the  mother  liquor  with  ether.  Yield  of  the  crude 
product  10-12  grammes.  It  crystallises  from  water  in  colourless 
lustrous  leaves.  M.P.  121°. 

(&)  2.4  grammes  of  magnesium,  20.4  grammes  of* iodobenzene 
and  40  c.c.  of  absolute  ether  are  converted  into  phenyl  mag- 
nesium iodide  as  in  (a).  The  product  is  cooled  and  carefully 
added,  drop  by  drop,  and  with  constant  shaking,  to  a  mixture  of 
10.6  grammes  of  freshly  distilled  benzaldehyde,  and  30  c.c.  of 
absolute  ether.  During  this  treatment  the  mixture  is  kept  cold 
with  ice  water.  A  violent  reaction  takes  place,  with  the  formation 
of  a  yellow,  and  finally  a  white,  precipitate.  The  reaction  mixture 
is  treated  with  ice  as  in  (a),  and  then  gradually  with  a  cooled 
mixture  of  15  c.c.  concentrated  hydrochloric  acid  in  an  equal 
volume  of  water.  It  is  extracted  with  commercial  ether.  In 
order  to  remove  benzaldehyde,  ±e  ethereal  layer  is  shaken 

i  B.  40,  1584. 


350  SPECIAL  PART 

thoroughly  with  a  dilute  water  solution  of  sodium  bisulphite. 
Upon  evaporating  the  ether  an  oily  reaction  product  is  obtained, 
which  solidifies  completely  when  it  is  cooled  and  rubbed  with  a 
glass  rod.  It  is  pressed  on  a  porous  plate  and  crystallised  from 
ligroin.  Yield  of  the  crude  product  10-14  grammes.  Benzhydrol 
forms  colourless  needles  which  melt  at  68°. 

With  brombenzene  and  magnesium  the  experiment  is  carried 
out  in  the  following  manner  :  2.4  grammes  of  magnesium  are 
covered,  in  the  presence  of  a  granule  of  iodine,  with  a  mixture 
of  15.7  grammes  of  brombenzene  that  must  be  perfectly  dry  and 
must  possess  a  constant  boiling  point,  and  50  c.c.  of  absolute 
ether.  If  the  materials  used  were  pure  and  perfectly  dry,  the 
reaction  will  commence  in  a  short  time  when  the  mixture  is 
heated  on  a  water-bath  as  in  (a),  i.e.  the  ether  will  continue  to 
boil  when  the  water-  bath  is  removed.  Almost  all  the  magnesium 
goes  into  solution  after  ^-1  hour,  and  the  boiling  of  the  ether 
ceases.  It  is  now  heated  moderately  on  the  water-bath  for  a 
quarter  of  an  hour.  The  treatment  with  benzaldehyde  is  exactly 
the  same  as  with  phenyl  magnesium  iodide. 

We  are  indebted  to  Grignard  for  the  important  observation  that  mono- 
brom  or  monoiodo  derivatives  of  different  hydrocarbons  (i  molecular 
weight)  unite  with  magnesium  (i  atomic  weight)  in  the  presence  of 
absolute  ether,  e.g.  : 


CH3I  +  Mg  = 

Methyl  magnesium  iodide 


C2H,,Br  +  Mg  =  Mg< 

xBr 

Ethyl  magnesium  bromide 

With  long  carbon  chains  in  the  aliphatic  series,  saturated  hydro- 
carbons are  also  formed,  and  the  longer  the  chain  the  more  readily 
will  this  reaction  take  place.  With  molecules  containing  six  or  more 
carbon  atoms,  the  main  reaction  consists  in  the  removal  of  halogen,  and 
the  formation  of  the  hydrocarbon  : 

2  C6H13.Br  +  Mg  =  MgBr2  +  CUHM. 


AROMATIC   SERIES  351 

In  an  analogous  way  are  formed  C6H  5  .  Mg  .  Br  and  C6H  .  .  Mg  .  I  = 
phenyl  magnesium  bromide  and  iodide  ;  C6H5  .  CH2  .  Mg.  I  =  benzyl 
magnesium  iodide  ;  C6HU  .  Mg  .  I  —  hexahydrophenyl  magnesium  io- 
dide (from  iodocyclohexamethylene),  etc.  Since  these  compounds  are 
formed  only  in  the  presence  of  ether  as  solvent,  it  is  probable  that  the 
ether  not  only  serves  as  a  solvent,  but  also  plays  an  essential  part  in 
the  reaction.  As  a  matter  of  fact  a  compound  C2H5  .  Mg  .  I  +  (C2H5)2O 
has  been  isolated  which  may  be  regarded  as  an  oxonium  derivative  : 


CJA*\L 

CaH,/    N 

The  alkyl  magnesium  haloids  or  their  ether  derivatives  are  soluble 
in  ether. .  On  account  of  their  unusual  reactivity  they  may  be  used  gen- 
erally for  the  synthetic  preparation  of  a  large  number  of  compounds. 
Thus  hydrocarbons  may  be  obtained  when  organo-magnesium  com- 
pounds are  treated  with  water  or  other  substances  containing  the 
hydroxyl  group,  e.g. : 

A 


Hydrocarbons  are  likewise  obtained  synthetically  by  the  action  of  alkyl 
sulphates,  e.g.  : 

/Br 
C6H5  .  Mg  .  Br  +  S04(CH3)2  =  QH5  .  CH3  +  Mg<f 

XO.S03CH3 

[n  the  synthesis  of  alcohols  (mentioned  below)  hydrocarbons  of  the 
ethylene  series  are  formed,  either  as  by-products,  or  as  main  products. 

They  unite  with  aldehydes  to  form  double  compounds,  which  are 
decomposed  with  water,  yielding  secondary  alcohols  •,  eg.  : 

/H 
C6H5.Mg.I  =  CeH4.cA).Mg.I, 

CH 


. 

C6H5  .  CO  .  |Mg.I  +  HO|  H  =  Mg<          +  C 


Basic  mag-  OH 

nesiuin  iodide     Diphenyl  carbinol 
or  benzhydrol 

This  reaction  was  carried  out  above  in  (b). 

When  the  simplest  aldehyde  (formaldehyde)  is  used  in  the  form  of 
its  polymer?  trioxymethylene,  primary  alcohols  are  formed. 

In  an  analogous  manner,  tertiary  alcohols  are  formed  when  ketones 
are  used,  e.g. : 


352  SPECIAL   PART 

/rv**'*J 


Acetophenone 


H3  NOH        VCH, 

XOH 

Phenyl -dimethyl 
carbinol 

The  esters  of  mono-  and  poly-basic  carbonic  acids  also  react  readily 
with  alkyl  magnesium  haloids  with  the  formation  of  alcohols.  In  this 
case,  two  molecules  of  the  magnesium  compound  react  with  one  molecule 
of  the  ester.  Thus  from  the  esters  of  formic  acid  secondary  alcohols  are 
formed,  e.g.: 

'H  /O.Mg.Br 

+  C2H5.Mg.Br  =  C< 

CTT  VY"    "PT 

2H5  \(-2hl5 

Ethyl  formate  OC2H5 

/H 

.  Mg .  Br 


/ 

a ,  /Br  /O 

)CaH,+  Br.Mg^1  C0H5  =  Mg<  +  C< 

—      ^~^    "    '  ^nr1  w          xV' 

OCi**«         \c 


O.Mg.Br 
2H5 


/Br  /C2H5 

.Mg.Br+HOH  =  Mg<        +  C< 
XOH        VH 

H5  XOH 

fj  Diethyl  carbinol 

In  an  analogous  manner  the  esters  of  all  the  other  monobasic  acids 
form  tertiary  alcohols.  Thus  ethyl  acetate  forms  with  ethyl  magnesium 
bromide  : 


=  Methyl  diethyl  carbinol. 


The  reaction  amounts  essentially  to  the  replacement  of  the  carbonyl 
oxygen  atom  of  the  corresponding  free  acid  by  two  univalent  hydrocarbon 
residues.  In  this  way,  the  esters  of  dibasic  acids  yield  diacid  alcohols  j 
Thus  from  oxalic  ester  is  formed  : 


AROMATIC  SERIES.  353 

H3 

Tetramethyl  glycol,  or  Pinacone. 


In  place  of  acid  esters  the  corresponding  chlorides  or  anhydrides 
may  also  be  used. 

As  has  already  been  mentioned,  in  the  synthesis  of  alcohols,  unsatu- 
rated  hydrocarbons  are  also  formed  in  addition  to  alcohols,  either  as 
by-products,  or  as  main  products.  These  are  formed  by  the  removal 
of  water  from  alcohols,  e.g.  : 


=  H20  +  |1 
H3  CH2 

H 

When  organo-magnesium  compounds  are  allowed  to  react  with  excess 
of  formic  ester,  aldehydes  are  formed,  and  not  secondary  alcohols,  e.g. : 

A 
C6H3 .  Mg .  I  +  H .  CO .  OC2H5  =  C6H5 .  CHO  +  Mg<^ 

OC2H5 

The  same  reaction  will  take  place  when,  instead  of  formic  ester,  ortho- 
formic  ester,  disubstituted  formamide,  and  other  derivatives  of  formic 
acid  are  used. 

Nitriles  unite  with    alkyl  magnesium  haloids  to  form  compounds 
which  yield  ketones  when  they  are  decomposed  with  water : 

/C6H5 
C6H5C=N  +  CH3 .  Mg .  I  =  C=N  .  Mg .  I. 

Benzonitrile  ^CH3 

/C,H.  /C6H5 

C=N.Mg.I  +  HOH  =  I.Mg.OH  +  C=NH, 

\CH3  \CH3 

C=NH  +  H2O  =  NH3  +  C6H5 .  CO  .  CH3. 

\CH  Acetophenone 

When  alkyl  magnesium  haloids  are  treated  with  dry  carbon  dioxide, 
carbonic  acids  are  formed,  e.g. : 

CHg.Mg.H-  C02  =  CH3.COOMgI, 
CH3.COOMgI  +  HOH  =  I.Mg.OH  +  CH3.COOH, 
or,  according  to  the  experiment  under  (a)  : 


354  SPECIAL  PART 

C6H5 .  Mg .  1  +  C02  =  C6H5 .  COOMgl, 
C6H5  .  COOMgl  +  HOH  =  I .  Mg  .  OH  +  C6H5 .  COOH. 

Thus  from  the  bromide  or  iodide  of  a  hydrocarbon  the  monocarbonic 
acid1  of  the  next  higher  series  is  formed. 

These  simple  examples  are  sufficient  to  show  the  great  importance 
of  the  Grignard  reaction.  Further  details  may  be  obtained  from  Jul. 
Schmidt's  work  on  "Die  organischen  Magnesium-verbindungen  und 
ihre  Anwendung  zu  Synthesen  I  u.  II  "  (Stuttgart,  Enke  ;  1905  u.  1908). 

41.   REACTION:   PREPARATION  OF   A  DYE   OF   THE  MALACHITE 
GREEN   SERIES 

EXAMPLE  :    Malachite  Green   from  Benzaldehyde   and   Dimethyl- 
aniline2 

(a)  Preparation  of  the  Leuco-Base.  — A  mixture  of  50  grammes 
of  dimethylaniline  and  20  grammes  of  benzaldehyde  (both  freshly 
distilled)  is  heated  in  a  porcelain  dish,  with  frequent  stirring,  on 
the  water-bath,  for  4  hours,  with  20  grammes  of  zinc  chloride, 
which  has  been  previously  fused  in  a  porcelain  dish,  and  pulver- 
ised, after  cooling.  (See  p.  358.)  This  viscous  mass,  which  can- 
not be  poured  directly  out  of  the  dish,  is  melted  by  covering  it 
with  hot  water,  and  heating  it  at  the  same  time  on  the  water-bath  ; 
while  hot,  it  is  transferred  to  a  ^-litre  flask.  Steam  is  conducted 
into  it,  until  no  drops  of  it  pass  over.  There  is  thus  obtained  the 
non-volatile  leuco-base  of  the  dye,  in  the  form  of  a  viscous  mass, 
which  adheres  firmly  to  the  walls  of  the  distilling  flask.  After  the 
liquid  is  cold,  the  water  is  poured  off,  the  base  adhering  to  the 
sides  of  the  flask  is  washed  with  water  several  times,  and  then  dis- 
solved in  the  flask  with  alcohol,  on  the  water-bath.  After  filtering, 
the  solution  is  allowed  to  stand  over  night  in  a  cool  place,  upon 
which  the  base  separates  out  in  colourless  crystals ;  these  are  fil- 
tered off,  washed  with  alcohol,  and  dried  in  the  air  on  several 
layers  of  filter-paper.  By  concentrating  the  mother-liquor,  a 
second  crystallisation  may  be  obtained.  Should  the  base  not 
crystallise,  but  separate  out  in  an  oily  condition,  which  frequently 


1  Concerning  the  other  course  of  the  reaction  see  B.  40,  1584. 

2  A.  206,  83  ;  217,  250. 


AROMATIC   SERIES  355 

happens  after  a  short  standing  of  the  filtered  solution,  this  is  due 
to  the  fact  that  an  insufficient  amount  of  alcohol  has  been  used. 
In  this  case,  more  alcohol  is  added,  and  the  mixture  heated  until 
the  oil  is  dissolved. 

(b)  Oxidation  of  the  Leuco-base.  —  Dissolve  i  o  parts,  by  weight, 
of  the  completely  dry  leuco-base  by  heating  in  a  quantity  of 
dilute  hydrochloric  acid  corresponding  to  2.7  parts,  by  weight, 
of  anhydrous  hydrochloric  acid.  For  the  purpose,  dilute  pure 
concentrated  hydrochloric  acid  with  double  its  volume  of  water, 
determine  the  specific  gravity  of  the  diluted  acid,  and  refer  to  a 
table  to  find  out  how  much  anhydrous  acid  the  solution  contains, 
and  from  this  calculate  how  much  of  the  solution  must  be  taken 
in  order  to  get  the  required  amount  of  the  anhydrous  acid 
(2.7  grammes).  The  colourless  solution  of  the  leuco-base  is 
then  diluted  in  a  large  flask  with  800  parts,  by  weight,  of  water, 
and  treated  with  10  parts  of  40  %  acetic  acid  (sp.  gr.  1.0523), 
prepared  by  gradually  diluting  glacial  acetic  acid  with  water ;  the 
mixture  is  well  cooled  by  throwing  in  pieces  of  ice ;  then,  with 
frequent  stirring,  gradually  add  (during  5  min.)  a  quantity  of 
freshly  prepared  lead  peroxide  paste 1  corresponding  to  7.5  grammes 
of  pure  lead  peroxide.  The  peroxide  is  weighed  off  in  a  beaker, 
and  treated  with  a  quantity  of  water  sufficient  to  form  a  very  thin 
paste.  The  residue  remaining  in  the  beaker  after  the  first  empty- 
ing is  washed  out  with  water.  After  the  addition  of  the  peroxide, 
the  reaction-mixture  is  allowed  to  stand  five  minutes,  with  frequent 
shaking;  then  add  a  solution  of  10  parts  of  Glauber's  salt  and 
50  parts  of  water ;  the  solution  is  then  filtered  off  through  a  folded 
filter  from  the  precipitated  lead  sulphate  and  chloride.  The  filtrate 
is  treated  with  a  filtered  solution  of  8  parts  of  zinc  chloride  dis- 
solved in  as  small  a  quantity  of  water  as  possible  ;  then  a  saturated 
sodium  chloride  solution  is  added,  until  all  the  dye  is  precipitated. 
This  is  easily  recognised  by  bringing  a  drop  of  the  solution,  with 
a  glass  rod  on  a  piece  of  filter-paper ;  a  bluish  green  precipitate 
surrounded  by  a  circle  of  a  still  fainter  bright  green  colour  will  be 
formed.  The  precipitated  dye  is  filtered  off  with  suction,  washed 
with  a  little  saturated  sodium  chloride  solution,  and  pressed  out 

1  See  page  388. 


356 


SPECIAL  PART 


on  a  porous  plate.  In  order  to  purify  it  further,  it  may  be  dis- 
solved again  in  water ;  and  from  the  filtered  solution,  after  cooling, 
it  is  again  thrown  out  by  sodium  chloride. 

The  reaction  just  carried  out,  discovered  by  Otto  Fischer  in  1877,  is 
also  used  in  the  large  scale  for  the  preparation  of  Malachite  Green,  or 
Bitter  Almond  Green.  In  the  formation  of  the  leuco-base,  the  follow- 
ing reaction  takes  place : 

XC6 


C6H5.CH 


C(;H4.N(CH3)2  =  /  C6H4.N(CH3)2      „ 
C6H4.N(CH3)2 


H 


Tetramethyldiamidotriphenylmethane 
=  Leuco-base  of  Malachite  Green 

The  substance  thus  obtained  is  not  a  dye,  but  the  reduction  product 
of  the  real  dye,  which,  on  oxidation,  passes  over  to  the  dye.  Formerly, 
the  dye  formation  was  believed  to  take  place  in  accordance  with  the 
following  equation  : 


/ 

/ 
< 


C6H4.N(CH3)2 
<C6H4.N(CH3)2|.H|C1 

H 


+H20. 


The  union,  effected  by  the  oxidation  between  the  pentavaient  nitrogen 
atom  of  the  dimethyl  aniline  residue  and  the  common  methane-carbon 
atom,  was  considered  to  be  the  condition  which  determined  the  nature 
of  the  dye.  At  present,  the  view  that  the  latter  is  determined  by  the 
presence  of  the  quinone-like  secondary  benzene  residue  is  generally 
accepted,  and  the  formula  of  the  dye-salt  is  written  thus : 


AROMATIC   SERIES  357 

Further,  it  may  be  pointed  out  in  this  place  that,  in  the  formation  ot 
the  leuco  base,  the  hydrogen  atom  in  the  para  position  to  the  dimethyl- 
amido  groups  N(CH3)2  unites  with  the  aldehyde  oxygen  atom  to  form 
water.  The  salt  of  the  formula  given  above  is  difficult  to  separate 
from  its  solution.  But  if  zinc  chloride  is  added,  a  double  salt  of  the 
same  colour  is  formed : 

3(C,3H,5N2C1)  +  2  ZnCl2  +  H2O 

which  may  be  separated  from  its  water  solution  by  common  salt. 

Malachite  Green  may  also  be  made  by  a  second  method,  which  was 
discovered  by  Dobner:  it  consists  in  heating  benzotrichloride  with 
dimethyl  aniline  in  the  presence  of  zinc  chloride: 


•  C6H4.N(CH3)2       /  C6H4.N(CH3)2 
.C6H4.N(CH3)2      \XH4.N(CH3)2 
XC1 

Since  the  chlorine  atom  remaining  over  migrates  toward  a  nitrogen 
atom,  the  dyestufF  salt  is  directly  formed  by  the  transformation.  Still, 
since  the  preparation  of  pure  benzotrichloride  on  the  large  scale  is  diffi- 
cult, this  method,  which  was  formerly  used,  has  been  abandoned,  and 
the  dye  is  now  prepared  exclusively  by  Fischer's  method. 

Malachite  Green  is  a  representative  of  a  whole  series  of  dyes,  —  the 
Malachite  Green  Series.  If,  instead  of  dimethyl  aniline,  diethyl  aniline 
is  used,  an  analogous  substance,  which  bears  the  name  of  Brilliant 
Green,  is  formed.  In  place  of  benzaldehyde,  substituted  benzalde- 
hydes,  etc.,  can  be  used.  The  dyes  of  the  Bitter  Almond  Series  colour 
only  the  animal  fibres,  silk  and  wool,  directly.  Vegetable  fibre  (cot- 
ton) is  not  coloured  unless  it  has  been  previously  mordanted. 


42.  REACTION:  CONDENSATION  OF  PHTHALIC  ANHYDRIDE  WITH 
A  PHENOL  TO  FORM  A  PHTHALEIN 

EXAMPLE:    (a)  Fluorescein.1     (b}  Bromination  of  Fluorescein 
with  the  Formation  of  Eosin 

(a)  In  a  mortar  grind  up  and  intimately  mix  15  grammes  of 
phthalic  anhydride  with  22  grammes  of  resorcinol,  and  heat  in  an 

1  A.  183, 1. 


358 


SPECIAL  PART 


oil-bath  to  180°  (Fig.  78).  As  a  vessel  for  heating  the  mixture 
an  "extract  of  beef"  jar,  glazed  inside,  is  well  adapted  to  the 
purpose ;  it  can  be  obtained  readily  at  a  small  cost,  and  may  be 
used  several  times  for  the  same  fusion.  It  is  suspended  by  its 
projecting  edge  from  a  triangle  into  the  oil-bath.  To  the  fused 

mass  add,  with  stirring  (glass  rod), 
in  the  course  of  10  minutes,  7 
grammes  of  pulverised  zinc  chlo- 
ride. This  is  prepared  in  the 
following  way  :  10  grammes  of  the 
commercial  salt,  which  always  con- 
tains water,  is  carefully  heated  to 
fusion  over  a  free  flame  in  a  por- 
celain dish.  After  the  mass  has 
been  kept  in  a  fused  condition  for 
a  few  minutes,  it  is  allowed  to  cool, 
and  the  solidified  subsiance  is  re- 
moved from  the  dish  with  a  knife 
and  pulverised.  After  adding  7 
grammes  of  the  anhydrous  salt 
thus  obtained,  the  temperature  is 
increased  to  210°,  and  the  heating 
continued  until  the  liquid,  which 
gradually  thickens,  becomes  solid, 
for  which  about  1-2  hours  is  required.  The  cold  friable  melt 
is  removed  from  the  crucible  with  a  sharp  instrument  (it  is  best 
to  use  a  chisel),  finely  pulverised,  and  boiled  10  minutes  in  a 
porcelain  dish  with  200  c.c.  of  water  and  10  c.c.  of  concentrated 
hydrochloric  acid.  This  causes  the  solution  of  the  substance 
which  did  not  enter  into  the  reaction ;  the  addition  of  hydro- 
chloric acid  is  necessary  to  dissolve  the  zinc  oxide  and  basic 
zinc  chloride.  The  fluorescem  is  filtered  from  the  solution, 
washed  with  water  until  the  filtrate  no  longer  gives  an  acid 
reaction ;  it  is  then  dried  on  the  water-bath.  Yield,  almost 
quantitative. 

(£)   Over  15  grammes  of  fluorescein  in  a  flask,  pour  60  grammes 


FIG.  78. 


AROMATIC  SERIES 


359 


of  alcohol  (about  95  %),  add,  with  frequent  shaking,  33  grammes 
of  bromine,  drop  by  drop,  from  a  separating  funnel.  This  should 
require  about  a  quarter-hour.  In  place  of  a  separating  funnel,  it 
is  advisable,  as  in  all  cases  of  bromination,  to  use  a  burette,  by  which 
the  troublesome  weighing  of  bromine  is  obviated.  Since  the  spe- 
cific gravity  of  bromine  at  moderate  temperatures  is  very  nearly  3, 
it  is  only  necessary  to  divide  the  required  weight  by  3,  in  order  to 
find  the  number  of  cubic  centimetres  corresponding  to  the  weight. 
Of  the  numerous  kinds  of  burettes,  the  one  best  adapted  to  this 


FIG.  79. 


FIG.  80. 


purpose  is  the  Winckler  form ;  since  it  possesses  no  cock,  it  can 
be  inserted  into  the  body  of  a  flask  with  a  not  too  narrow  neck, 
and  by  this  manipulation  the  disagreeable  bromine  vapours  may 
be  avoided  (Fig.  79).  In  the  above  case,  n  c.c.  of  bromine 
are  necessary.  On  the  addition  of  bromine,  it  is  observed  that  the 
quantity  of  fluorescein  insoluble  in  alcohol  steadily  decreases,  and 
that  when  about  one -half  of  the  bromine  has  been  added,  a  clear, 
dark,  reddish-brown  solution  is  formed.  This  is  due  to  the  fact 
that  the  dibromide  is  first  formed,  which  is  easily  soluble  in 


360  SPECIAL  PART 

alcohol.  On  the  further  addition  of  bromine,  the  tetra-bromide 
is  formed,  which,  since  it  is  difficultly  soluble  in  alcohol,  separates 
out  in  the  form  of  brick-red  leaflets.  After  all  the  bromine  has 
been  added,  the  reaction-mixture  is  allowed  to  stand  for  2  hours, 
the  precipitate  is  filtered  off,  washed  several  times  with  alcohol, 
and  dried  on  the  water-bath.  The  product  thus  obtained  is  a 
compound  of  i  molecule  of  eosin  and  i  molecule  of  alcohol.  In 
order  to  obtain  pure  eosin  from  it,  the  substance  is  heated  a  half- 
hour  in  an  air-bath  at  110°  :  during  the  heating,  its  colour  becomes 
brighter.  Since  eosin  is  insoluble  in  water,  the  soluble  potassium-, 
sodium-,  or  ammonium-salt  is  prepared  on  the  large  scale  for  dyeing. 
Ammonium  Eosin.  —  Over  a  flat-bottom  crystallising  dish,  \ 
filled  with  a  concentrated  ammonia  solution,  place  a  filter,  of  paper 
as  strong  as  possible.  Upon  this  is  spread  the  eosin  acid,  in  a 
layer  about  \  cm.  thick,  and  the  whole  is  covered  with  a  funnel 
(Fig.  80).  The  bright-red  crystals  of  the  free  eosin  acid  very 
soon  assume  a  darker  colour,  and,  after  about  three  hours,  it  is  com- 
pletely converted  into  the  ammonium  salt,  which  forms  dark-red 
crystals  with  a  greenish  lustre.  The  end  of  the  reaction  is  easily 
recognized,  by  testing  a  small  portion  with  water.  If  it  dissolves, 
the  conversion  is  complete. 

On  the  large  scale,  this  reaction  is  carried  out  in  wooden  chests 
containing  a  number  of  frames  covered  with  coarse  linen,  arranged 
like  drawers.  After  the  eosin  is  spread  out  on  the  linen  in  thin  layers, 
dry  ammonia  evolved  from  ammonium  chloride  and  lime  is  passed  into 
the  chest,  until  a  test-portion  of  the  substance  will  completely  dissolve. 

Sodium  Eosin.  —  Grind  6  grammes  of  eosin  with  i  gramme  of 
dehydrated  sodium  carbonate,  and  in  a  not  too  small  beaker 
moisten  it  with  a  little  alcohol;  after  the  addition  of  5  c.c.  of 
water,  heat  on  the  water-bath  until  the  evolution  of  carbon  dioxide 
ceases.  To  the  water  solution  of  sodium  eosin  thus  obtained,  add 
20  grammes  of  alcohol,  heat  to  boiling,  and  filter  the  hot  solution. 
On  cooling,  the  soluble  sodium  salt  sepafates  out  in  the  form  of 
splendid,  brownish- red  needles  of  a  metallic  lustre.  As  is  the 
case  with  many  dyes,  the  crystallisation  requires  a  long  time ;  one 
day,  at  least,  is  necessary. 


AROMATIC  SERIES  361 

Phthalic  anhydride  and  phenols  can  react  with  each  other  in  two 
different  ways,  (i)  An  equal  number  of  molecules  of  each  can  con« 
dense,  the  oxygen  atom  of  the  anhydride,  which  unites  the  carbonyl 
groups,  can  combine  with  two  ring-hydrogen  atoms  of  the  phenol  to 
form  one  molecule  of  water ;  this  action  results  in  the  formation  of  an 
anthraquinone  derivative : 

/CO  /CO\ 

QH/    >|0  +  Hj .  CCH3 .  OH  =  C6H/         >C6H3 .  OH  +  H..O 

N:o  \co/ 

Phenol  Oxyanthraquinone 

Or  (2)  one  molecule  of  the  anhydride  can  react  with  two  molecules  of 
the  phenol  in  such  a  way  that  one  of  the  two  carbonyl-oxygen  atoms 
of  the  former  combines  with  one  ring-hydrogen  of  the  two  phenol 
molecules  to  form  a  so-called  phthalem: 

HO        OH 

H|.C6H4.OH  |          | 

,£  |0  +  H  . C6H4 .  OH  C6H4  C6H4 


<     >0 

x:D 


=       V 

C6H4< 


Phenolphthale!n= 
dioxyph  thalophenone 

For  the  knowledge  concerning  this  class  of  compounds,  to  which  be- 
long numerous  important  dyestuffs,  we  are  indebted  to  the  investiga- 
tions of  A.  Baeyer  (1871).  Phthalophenone  is  considered  to  be  the 
mother-substance  of  the  group  : 


which,  as  already  stated,  is  obtained  from  phthalyl  chloride  and  benzene 
in  the  presence  of  aluminium  chloride.  If  one  conceives  that  the 
mother-substance  can  take  up  one  molecule  of  water,  a  hypothetical 
mono-carbonic  acid  of  triphenyl  carbinol  would  result  : 


4.CO.OH, 


6 
X)H 


3^2  SPECIAL  PART 

the  formula  of  which  shows  very  clearly  the  connection  between  the 
phthalei'ns  and  the  triphenyl  methane  derivatives. 

If,  as  expressed  by  the  above  equation,  phthalic  anhydride  is  allowed 
to  act  on  phenol,  phenolphthaleiin  is  obtained,  a  substance  of  acid 
properties,  colourless  in  the  free  condition ;  its  salts  are  red.  It  is 
used  as  an  indicator  in  volumetric  analysis. 

By  the  action  of  phthalic  anhydride  on  resorcinol,  the  formation  of 
a  tetraoxyphthalophenone  would  naturally  be  expected ;  but  fluorescein, 
containing  the  constituents  of  one  molecule  of  water  less  than  this,  is 
obtained,  an  inner  anhydride  formation  taking  place  between  the  two 
hydroxyl  groups : 

£>H         HO  OH 

IOHI 

UH-\/    -    - 

+  2H20. 

C6H4<^>0 

Fluorescein 

Fluorescein  is  technically  prepared  on  the  large  scale  by  the  method 
given  above.  While  phenolphthalein,  in  spite  of  the  intense  colour 
of  its  salts,  is  not  a  dye,  in  that  it  does  not  colour  fibres,  fluorescein  is 
a  true  dye  which  colours  animal  fibres  a  fast  yellow.  But  it  is  not 
manufactured  as  a  dye,  since  it  has  been  replaced  by  other  dyes  that 
give  as  beautiful  colours  and  are  cheaper.  A  number  of  its  halogen- 
and  nitro-substitution  products  have  valuable  colouring  properties,  and 
are  prepared  from  it.  The  simplest  dye  of  this  kind  is  eosin  or  tetra- 
brom-fluorescein,  discovered  in  1874  by  Caro.  The  four  bromine 
atoms  are  equally  divided  between  the  two  resorcinol  residues : 

HO  ~  OH 

I 
C6HBr/\C6HBr2 

C6H, 


which  follows  from  the  fact  that  eosin  in  fusion  with  potassium  hydrox- 
ide yields  di-bromresorcinol  besides  phthalic  acid.  Instead  of  phthalic 
anhydride,  the  di-  and  tetra-chlor-substitution  products  are  fused  with 


AROMATIC  SERIES 


363 


resorcinol  on  the  large  scale  ;  and  so  there  is  obtained  in  the  phthalic 
acid  residue,  the  di-  and  tetra-chlorfluoresce'ins  from  which  halogen  sub- 
stitution products,  nitro-derivatives,  ethers,  etc.,  are  prepared  on  the 
large  scale  (Phloxine,  Rose  Bengal). 

Besides  fluorescein  there  is  practically  only  one  other  phthalein 
prepared  technically,  Galleiin.  This  is  done  by  heating  phthalic  anhy- 
dride with  the  ^-trioxybenzene  —  pyrogallol.  In  this  case  the  same 
anhydride  formation  takes  place  as  in  the  preparation  of  fluorescein : 

CO 

>0    /OH 

— C6HQ^OH  =  Galleiin. 
X) 


From  gallein,  a  derivative  of  anthracene,  coerulein,  a  new  dye,  is  ob- 
tained by  heating  with  sulphuric  acid.  Since  1887  the  phthaleins  have 
been  on  the  market  under  the  name  of  rhodamines,  which  are  prepared 
in  a  manner  similar  to  that  of  fluorescein,  except  that  instead  of 
resorcinol,  m-amidophenol,  or  amidophenols  substituted  by  alkyls  in 
the  amido-group,  are  used  : 

/NH2 
CM  ' 


H0N 


NH 


NH.; 


C6H4 


Simplest  Rhodamine 

The  rhodamine  on  the  market  is  the  tetra-ethyl  derivative  of  this 
mother-substance . 


364  SPECIAL   PART 


43.  REACTION:    CONDENSATION   OF  MICHLER'S   KETONE  WITH  AN 
AMINE   TO  A  DYE  OP  THE   FUCHSINE   SERIES 

EXAMPLE:   Crystal  Violet  from  Michler's  Ketone  and  Dimethyl 

Aniline 

A  mixture  of  25  grammes  of  dimethyl  aniline,  10  grammes  of 
Michler's  ketone  (this  is  on  the  market),  and  10  grammes  of 
phosphorus  oxychloride,  is  heated  in  an  open,  dry  flask,  5  hours, 
on  an  actively  boiling  water-bath.  The  blue-coloured  mass  is 
then  poured  into  water,  made  alkaline  with  a  solution  of  caustic 
soda,  and  treated  with  steam  until  no  drops  of  the  unattacked 
dimethyl  aniline  pass  over.  After  cooling,  the  solidified  colour- 
base  remaining  in  the  distillation  flask  is  filtered  from  the  alkaline 
solution,  washed  with  water,  and  boiled  with  a  mixture  of  i  litre 
of  water  and  5  grammes  of  concentrated  hydrochloric  acid.  The 
blue  solution  is  filtered  while  hot  from  the  colour-base,  which 
remains  undissolved  ;  the  latter  is  boiled  again  with  a  fresh  quan- 
tity of  dilute  hydrochloric  acid ;  this  operation  is  repeated  until 
the  substance  has  been  almost  entirely  dissolved.  After  cooling, 
the  solution  of  the  dye  is  treated  with  finely  pulverised  salt 
(stirring)  until  the  dye  is  precipitated.  It  is  then  filtered  with 
suction,  pressed  out  on  a  porous  plate,  and  crystallised  from  a 
little  water.  On  cooling,  the  Crystal  Violet  separates  out  in 
coarse  crystals  of  a  greenish  colour  j  these  are  filtered  off  and 
dried  in  the  air  on  filter-paper. 

If  Michler's  ketone  is  heated  with  an  amine  in  the  presence  of  a 
condensation  agent  (phosphorus  oxychloride,  POC13),  addition  takes 
place,  in  accordance  with  the  following  equation : 

C6H4.N(CH3)2  C6H4.N(CH3), 

CO  +  H.C6H4.N(CH3)2=C<^'N(CH3)2 

\LfiH4.N(LH3)2 
.N(CH3)S 

Michler's  ketone  Hexamethylpararosaniline  = 

Colour-base  of  Crystal  Violet 


AROMATIC  SERIES 


365 


If  this  is  dissolved  in  hydrochloric  acid,  one  molecule  of  this  is  added, 
and,  as  in  the  formation  of  Malachite  Green,  the  elimination  of  a  mole* 
cule  of  water  immediately  takes  place  and  the  dye  is  formed  : 

N(CH3)a 
N(CH8), 


P4.N(CHa), 

SH4.N(CH3)2 
.H4.N(CH3)2C1 


or 


Crystal  Violet 

It  is  a  derivative  of  parafuchsine  : 

6H4.NH2 
H4.NH2 
H4.  NH2CJ 


or 


C6H4.NH2 


.  Cl 


indeed,  it  may  be  considered  as  a  hexamethyl  parafuchsine.  It  is  pre- 
pared technically  in  the  same  way,  and  forms  the  principal  constituent 
of  the  Methyl  Violet  obtained  by  the  oxidation  of  dimethyl  aniline. 

Dyes  can  also  be  prepared  in  the  same  way  by  the  combination  of 
other  amines  with  Michler's  ketone,  of  which  it  is  only  possible  to 
mention  here  Victoria  Blue  and  Night  Blue. 

44.    REACTION:    CONDENSATION    OP   PHTHALIC    ANHYDRIDE   WITH 
A  PHENOL  TO  AN  ANTHRAQUINONE  DERIVATIVE 

EXAMPLE  :   Quinizarin  from  Phthalic  Anhydride  and 
Hydroquinone  l 

A  mixture  of  5  grammes  of  pure  hydroquinone  and  20  grammes 
of  phthalic  anhydride  is  heated  in  an  open  flask  with  a  mixture 
of  100  grammes  of  pure  concentrated  sulphuric  acid  and  10 


l  B.  6,  506;  8,  152;  A.  212.  lo. 


366  SPECIAL  PART 

grammes  of  water  for  3  hours  in  an  oil-bath  to  170-180°,  and 
finally  for  i  hour  at  190-200°.  The  directions  as  to  time  and  tem- 
perature must  be  followed  as  exactly  as  possible.  The  hot  solution 
is  poured,  with  stirring,  into  about  400  c.c.  of  water  in  a  porcelain 
dish,  heated  to  boiling,  and  filtered  hot  with  the  aid  of  a  Biichner 
funnel.  The  residue  remaining  on  the  filter  is  again  boiled  out 
with  water  and  filtered  while  hot.  In  order  to  separate  the  quini- 
zarin  from  carbonaceous  decomposition  products,  the  precipitate 
is  boiled  with  200  c.c.  of  glacial  acetic  acid,  filtered  hot  with 
suction,  the  filtrate  poured  into  a  beaker,  and,  while  hot,  treated 
with  its  own  volume  of  hot  water.  The  residue  remaining  on  the 
filter  is  again  boiled  up  with  100  c.c.  glacial  acetic  acid,  and,  after 
filtering,  treated  as  above.  On  cooling  of  the  diluted  acetic  acid 
solution,  the  crude  quinizarin  separating  out  is  filtered  off,  washed 
with  water  several  times,  dried  first  on  the  water-bath,  and  finally 
in  an  air-bath  at  120°.  Since  it  is  difficult  to  obtain  it  pure  by 
crystallisation,  after  drying  it  is  distilled  from  a  small  retort  of 
difficultly  fusible  glass,  and  is  driven  over  as  rapidly  as  possible 
with  a  large  flame.  A  beaker  is  used  as  a  receiver.  It  is  more 
convenient  to  use  a  porcelain  mortar,  and  a  porcelain  dish  as  a 
cover.  After  the  distillate  in  the  receiver  and  that  in  the  neck  of 
the  retort  (this  is  broken)  has  been  finely  pulverized,  it  is  crystal- 
lized from  glacial  acetic  acid,  from  which,  on  cooling,  the  quinizarin 
separates  out  in  the  form  of  large,  orange-yellow  leaves  ;  these  are 
filtered  off  and  washed  with  glacial  acetic  acid,  which  is  steadily 
diluted  with  water,  until  finally  only  pure  water  is  used.  Better 
crystals  (dark-red  compact  needles)  may  be  obtained  by  dissolving 
the  distilled  quinizarin  in  toluene,  heated  on  a  water-bath.  The 
filtered  crystals  are  washed  first  with  toluene  and  then  with  alcohol. 

Under  the  preparation  of  fluoresce'in,  it  has  already  been  mentioned 
that  phthalic  anhydride  condenses  with  phenols  in  certain  proportions, 
to  form  derivatives  of  anthraquinone.  The  reaction  just  effected  takes 
place  in  accordance  with  the  following  equation  : 


/co\ /co\ 

[4\          >|0  +  H2.|CfiH2.(OH)2  =  Cr>H4<          >C6H2(OH)2 
\C(X  \CO/ 

Quinizarin 


AROMATIC   SERIES  367 

In  an  analogous  way,  mono-acid-  as  well  as  poly-acid  phenols,  condense 
with  phthalic  anhydride.  It  is  of  theoretical  importance  that  from 
pyrocatechol  (o-dioxybenzene),  besides  a  second  isomer,  alizarin  is 
obtained,  showing  that  the  two  hydroxyl  groups  in  alizarin  are  in  the 
ortho  position  to  each  other.  Of  practical  significance  is  the  above 
reaction  for  the  preparation  of  anthragallol,  which  is  obtained  on  the 
large  scale  by  heating  pyrogallol  with  phthalic  anhydride : 


H2|.C6H.(OH)3  =  C6H4<^      ^C6H.(OH)3  +  H,0. 

Pyrogallol  Trioxyanthraquinone  = 

Anthragallol 

It  may  be  mentioned  briefly  that  by  the  condensation  of  benzole 
acid  with  oxybenzoi'c  acids,  similar  compounds  are  also  obtained : 


Anthragallol 


Quinizarin  dissolves,  like  oxyanthraquinones,  in  alkalies  with  a 
violet  colouration.  (Try  it.) 

45.    REACTION:  ALIZARIN  FROM  SODIUM  p-ANTHRAQUINONE- 
MONOSULPHONATEi 

In  an  autoclave  or  an  iron  pipe  with  a  cap  which  can  be 
screwed  on  (see  page  69),  heat  a  mixture  of  10  parts  commercial 
sodium  anthraquinonemonosulphonate,  30  parts  of  sodium  hy- 
droxide, 1.8  parts  of  finely  pulverised  potassium  chlorate,  with  40 
parts  of  water,  for  20  hours  to  170°.  After  cooling,  the  melt  is 
boiled  out  with  water  several  times,  and  acidified  at  the  boiling- 
point  of  the  solution  in  a  large  dish  with  concentrated  hydro- 
chloric acid.  The  alizarin  separating  out  is  then  filtered  off 
according  to  the  quantity,  either  with  suction  or  with  the  aid  of 
a  filter-press,  washed  with  water,  pressed  out  on  a  porous  plate, 
and  dried  in  an  air-bath  at  120°.  In  order  to  obtain  it  com- 
pletely pure,  it  is  distilled  rapidly  from  a  small  retort,  and  is 


1  A.  Spl.  7,  300 ;  B.  3,  359 ;  9,  281, 


368  SPECIAL  PART 

crystallised  from  glacial  acetic  acid,  or  in  large  quantities  from 
nitrobenzene. 

The  sodium  hydroxide  fusion  of  the  sodium  anthraquinonemono- 
sulphonate  is  an  abnormal  reaction  to  the  extent  that  besides  the  re- 
placement of  the  sulphonic  acid  group  by  hydroxyl,  a  hydrogen  atom 
is  also  oxidised  to  a  hydroxyl  group : 


+  3  NaOH  +  O 

,Na 

)Na 


The  tendency  to  the  formation  of  alizarin  is  so  great  that  even  with- 
out the  addition  of  an  oxidising  agent  (potassium  chlorate  or  nitrate), 
it  is  formed  with  the  evolution  of  hydrogen.  Formerly  the  oxygen  of 
the  air  was  used  as  the  oxidising  agent,  the  reaction  being  effected 
in  air. 

In  order  to  prepare  alizarin  on  the  large  scale,  anthracene  is  the 
starting-point ;  this  is  obtained  from  the  highest-boiling  fractions  of 
coal  tar  (anthracene  oil).  It  is  oxidised  by  chromic  acid  to  anthra- 
quinone  (see  below),  and  this  on  heating  with  sulphuric  acid  is  con- 
verted into  the  monosulphonic  acid.  The  separation  of  this  latter 
compound  is  greatly  facilitated  by  the  fact  that  it  forms  a  sodium  salt 
difficultly  soluble  in  water,  which,  on  account  of  its  silvery  appearance, 
is  called  "  Silver  salt."  If  the  sulphonation  mixture  is  diluted  with 
water  and  neutralised  with  sodium  carbonate,  the  sodium  anthraquinone- 
monosulphonate  is  precipitated  directly,  which  thus  obviates  the  neces- 
sity of  removing  the  excess  of  sulphuric  acid  beforehand.  On  the  large 
scale  the  alizarin  fusion  is  conducted  exactly  as  on  the  small  scale, 
except  that  autoclaves,  with  stirring  attachments,  are  used.  The  con- 
stitutional formula  of  alizarin  is : 

OH 
CO 


The  salts  are  intensely  coloured.     The  red  aluminium  salt,  the 
violet  ferric  salt,  and  the  garnet-brown  chromic  salt  are  especially  im- 


AROMATIC   SERIES  369 

portant  in  dyeing  With  alizarin  and  all  its  related  compounds  the 
dyeing  is  effected  by  mordanting  the  fibre  with  a  salt  of  one  of  the 
three  oxides  just  mentioned;  the  thus  prepared  fibre  is  heated  with 
a  thin  dilute  water-paste  of  the  free  insoluble  dye,  whereby  salts  are 
formed  on  the  fibre  (Lakes). 

From  two  disulphonic  acids  of  anthraquinone,  two  trioxyanthra- 
quinones,  flavo-  and  anthra-purpurin,  are  prepared  in  a  manner  analo- 
gous to  that  by  which  alizarin  is  obtained  from  the  monosulphonic 
acid. 

From  alizarin  there  can  be  prepared,  further,  by  nitration,  the  a-  or 
/3-nitro-alizarin,  and  from  this,  by  reduction,  the  corresponding  amido- 
alizarin.  From  /?-nitro-  and  amido-aiizarin,  by  heating  with  glycerol 
and  sulphuric  acid,  the  important  Alizarin  Blue  is  obtained.  Further, 
by  the  action  of  fuming  sulphuric  acid  on  alizarin  there  is  obtained  a 
tetraoxyanthraquinone  (Bordeaux),  etc. 


46.   REACTION:  ZINC  DUST  DISTILLATION 
EXAMPLE:   Anthracene  from  Alizarin  or  Quinizarin 

To  a  paste  prepared  by  rubbing  up  100  grammes  of  zinc  dust 
with  30  c.c.  of  water,  add  pieces  of  porous  pumice  stone  of  a  size 
that  will  conveniently  pass  into  a  combustion  tube,  and  stir  them 
around  so  that  they  become  covered  with  the  zinc  dust  paste. 
They  are  removed  from  the  paste  with  pincers,  heated  in  a  porce- 
lain dish  over  a  free  flame  (in  constant  motion)  until  the  water  is 
evaporated.  A  combustion  tube  of  hard  glass  60-70  cm.  long 
is  drawn  out  at  one  end  to  a  narrow  tube,  the  narrowed  end  is 
closed  by  a  loose  plug  of  asbestos,  and  a  layer  of  zinc  dust  5  cm. 
long  is  placed  next  to  the  plug ;  then  follows  a  mixture  of  |-i 
gramme  of  alizarin  or  quinizarin  with  10  grammes  of  zinc  dust, 
and  finally,  a  layer  of  pumice-zinc  dust  30  cm.  long.  After  a 
canal  has  been  formed  over  the  zinc  dust,  by  placing  the  tube  in 
a  horizontal  position  and  tapping  it,  the  tube  is  transferred  to  a 
combustion  furnace  inclined  at  an  oblique  angle,  and  dry  hydrogen 
is  passed  through  the  tube  without  heating.  In  order  to  test 
whether  the  air  has  been  completely  expelled  from  the  tube,  the 

2  B 


3/0  SPECIAL   PART 

open  end  is  closed  by  a  cork  bearing  a  small  glass  tube  to  which 
is  attached  a  piece  of  rubber  tubing ;  the  gas  being  evolved  is 
conducted  into  a  soap  solution,  and  the  bubbles  formed  are 
ignited,  during  which  the  greatest  care  must  be  taken  to  keep 
the  flame  from  coming  in  contact  with  the  gas  issuing  from  the 
rubber  tubing,  otherwise  a  serious  explosion  may  result.  If  an 
explosion  accompanied  by  a  report  takes  place  when  the  bubbles 
are  ignited,  the  air  has  not  been  completely  removed,  but  if  they 
burn  quietly,  then  only  pure  hydrogen  is  present.1  When  this  is 
the  case,  the  current  of  gas  is  diminished  so  that  only  two  bubbles 
per  second  pass  through  the  wash-bottle;  the  pumice-zinc  dust 
is  then  heated  with  small  flames,  these  are  increased  in  size 
gradually,  and  finally,  the  tiles  being  placed  in  position,  it  is 
heated  as  strongly  as  possible ;  then  the  rear  layer  of  5  cm.  of 
zinc  dust  is  similarly  heated,  and  as  soon  as  this  glows,  as  in  the 
nitrogen  determination,  the  mixture  of  the  substance  and  zinc 
dust  is  gradually  heated.  The  anthracene  formed  condenses  to 
crystals  in  the  forward  cool  part  of  the  tube.  After  the  reaction 
is  complete,  while  the  tube  is  allowed  to  cool,  a  moderately  rapid 
current  of  hydrogen  is  passed  through  it ;  the  forward  part  of  the 
tube  containing  the  anthracene  is  broken  off  and  the  substance 
removed  with  a  small  spatula;  it  is  purifed  by  sublimation  in  a 
suitable  apparatus  (see  pages  14  and  15).  Melting-point,  213°. 
The  sublimed  anthracene  is  dissolved  by  heating  in  a  test- 
tube  with  a  little  glacial  acetic  acid ;  it  is  treated  with  about 
double  its  weight  of  chromic  anhydride,  and  heated  a  short  time 
to  boiling.  The  solution  is  then  diluted  with  several  times  its 
volume  of  water,  the  anthraquinone  separating  out  is  filtered  off, 
washed  with  some  dilute  sulphuric  acid,  then  with  water,  and  is 
finally  crystallised  in  a  test-tube  from  a  little  glacial  acetic  acid. 
Long  colourless  needles  of  anthraquinone,  which  melt  at  277°,  are 
thus  obtained. 


1  As  described  under  Carbon  Monoxide,  the  test  may  also  be  made  by  filling 
a  test-tube  with  the  gas  over  water,  and  applying  a  match  to  the  mouth  of  the 
tube. 


PYRIDINE   SERIES  3/1 

Zinc  dust  is,  especially  at  high  temperatures,  an  excellent  reducing 
agent  (Baeyer,  A.  140,  205),  which  can  be  used  for  the  reduction  of 
almost  all  aromatic  oxygen  compounds  derived  from  hydrocarbons,  e.g. : 

C6  H, .  OH  +  Zn  =  C6H6  +  ZnO 

Phenol  Benzene 

C10Hr .  OH  +  Zn  =  C10H8  +  ZnO 

Naphthol  Naphthalene 

Also  ketone-oxygen,  as. the  above  example  shows,  can  be  replaced 
by  hydrogen.  The  reaction  given  under  Alizarin  possesses  an  historical 
interest,  since,  by  means  of  it,  Gra'be  and  Liebermann,  in  1868,  dis- 
covered that  alizarin,  which  had  been  previously  obtained  from  madder 
root,  was  a  derivative  of  anthracene,  and  could  be  prepared  synthetically 
from  it.  (B.  i,  43.) 


III.     PYRIDINE   AND    QUINOLINE   SERIES 

1.   REACTION:   THE   PYRIDINE   SYNTHESIS   OF  HANTZSCHi 

EXAMPLE  :    Collidine  =  Trimethylpyridine 

Dihydrocollidinedicarbonic  Acid  Ester.  —  A  mixture  of  25 
grammes  of  acetacetic  ester  and  8  grammes  of  aldehyde-ammonia 
is  heated  in  a  small  beaker  on  a  wire-gauze,  about  three  minutes,  to 
loo-iio0,  the  mixture  being  stirred  with  the  thermometer.  The 
warm  reaction-mixture  is  then  treated  with  double  its  volume 
of  dilute  hydrochloric  acid,  and  stirred  vigorously  without  further 
heating  until' the  liquid  mass  solidifies.  It  is  then  thoroughly  tritu- 
rated in  a  mortar,  filtered,  washed  with  water,  and  dried,  either 
by  pressing  out,  or  by  warming  on  the  water-bath.  For  the  further 
working  up  of  the  collidinedicarbonic  acid  ester,  the  crude  product 
can  be  directly  used.  In  order  to  obtain  the  dihydroester  in  a 
crystallised  condition,  2  grammes  of  the  crude  product  are  dissolved 
in  a  small  quantity  of  alcohol  in  a  test-tube,  by  heat,  and  allowed 

i  A.  215,  i. 


372 


SPECIAL   PART 


FIG.  81. 


to  cool  slowly.  Colourless  tablets  with  a  bluish  fluorescence  are 
thus  obtained.  Melting-point,  131°. 

Collidinedicarbonic  Acid  Ester.  —  The  crude  dihydroester  is 
treated  in  a  small  flask  with  an  equal  weight  of  alcohol ;  complete 

solution  does  not  take  place. 
Into  the  mixture  cooled  by 
water  pass  nitrous  fumes  (Fig. 
81),  until  the  dihydroester  goes 
into  solution,  and  a  test-portion 
dissolves  to  a  clear  solution  in 
dilute  hydrochloric  acid.  The 
alcohol  is  then  evaporated  by 
heating  on  the  water-bath,  the 
thick  residue  is  treated  with  a 
sodium  carbonate  solution  to 
alkaline  reaction ;  the  oil  sepa- 
rating out  is  taken  up  with  ether. 
After  the  ethereal  solution  has 

been  dried  by  a  small  piece  of  potassium  hvdroxide,  or  potash, 
the  ether  is  evaporated,  and  the  residue  subjected  to  distillation  ; 
on  account  of  the  high  boiling-point  of  the  ester,  a  fractionating 
flask  is  selected,  having  the  condensation  tube  as  near  as  possible 
to  the  bulb.  The  fraction  passing  over  between  290-310°  can  be 
used  for  the  following  experiment : 

Potassium  Collidine  Dicarbonate.  —  The  saponification  of  the 
ester  is  effected  by  boiling  with  alcoholic  potash,  prepared  in  the 
following  manner  :  Finely  pulverised  potassium  hydroxide  (2  parts 
to  i  part  of  ester)  is  moderately  heated  in  a  flask  on  a  wire-gauze 
with  3  times  its  weight  of  absolute  alcohol,  until  the  greater  portion 
has  passed  into  solution.  The  alcoholic  solution  is  then  poured 
off  from  the  portion  remaining  undissolved,  treated  with  the  ester 
to  be  saponified,  and  heated  4-5  hours  on  a  rapidly  boiling  water- 
bath  (with  reflux  condenser)  ;  the  potassium  salt  separates  out  in 
crusts.  The  alcoholic  liquid  is  then  poured  off  from  the  salt, 
and  the  latter  washed  on  the  filter  with  alcohol  and  finally  with 
ether. 


PYRIDINE   SERIES  373 

Collidine.  —  The  dried  potassium  salt  is  intimately  mixed  in  a 
mortar  with  double  its  weight  of  slaked  lime,  and  placed  in  one 
end  of  a  hard  glass  tube  (about  2  cm.  wide  and  55  cm.  long). 
In  order  to  prevent  the  mixture  from  being  carried  over  into  the 
receiver  on  heating,  a  small,  loose  plug  of  asbestos  is  placed  in  the 
tube  in  front  of  it.  After  a  canal  has  been  made  by  tapping, 
the  tube  is  connected  with  an  adapter  bent  downwards,  by  means 
of  a  cork  or  asbestos  paper ;  it  is  then  transferred  to  a  combustion 
furnace,  the  rear  end  of  which  is  somewhat  elevated  and  warmed 
throughout  its  entire  length  with  small  flames,  beginning  at  the 
closed  end.  The  flames  are  steadily  increased  in  size  until,  with 
the  tiles  in  position,  the  tube  is  heated  as  strongly  as  possible. 
The  collidine  passing  over  is  taken  up  with  ether,  dried  with 
potassium  hydroxide,  and,  after  the  evaporation  of  the  ether,  is 
subjected  to  distillation.  Boiling-point,  172°. 

On  heating  acetacetic  ester  with  aldehyde-ammonia,  the  following 
reaction  takes  place  (see  A.  215,  8)  : 

CHS 


OCH 


C2H5O.OC.C  C.CO.OQHs 

QHgO.OC.CHjj         CHg.CO.OQHs  = 

CH3— C  C— CH3 

CH3.CO  CO.CH3  \XT/ 

HNH2  N 

H  +3H20. 

Dihydrocollidinedicarbonicethyl  ester 

The  reaction  may  be  modified  by  using  other  aldehydes  instead  of  acet- 
aldehyde ;  thus  there  is  obtained  from  benzaldehyde,  acetacetic  ester, 
and  ammonia,  the  dihydrophenyllutidinedicarbonic  ester: 

C*  TJ  CgHs 

^e^lg  I 

OCH  /°H\ 

C2H5O .  OC— CH2         CH2— CO .  OC2H6  =  QHsO .  OC— C  C— CO .  OC2H 

CH8— CO  CO— CH3  H8C— C  C— CH3 

NH2H  XTVTTI/ 


374  SPECIAL   PART 

With  proprionic  aldehyde,  butyraldehyde,  valeraldehyde,  oenanthol, 
myristic  aldehyde,  nitrobenzaldehyde,  phenylacetaldehyde,  furfurol, 
.md  others,  the  reaction  can  be  carried  out.  All  the  compound* 
obtained  contain  the  methyl  groups  of  the  two  acetacetic  ester  mole- 
cules, but  the  third  side-chain  is  different,  depending  upon  the  nature 
of  the  aldehyde  employed. 

By  passing  nitrous  fumes  into  an  alcoholic  solution  of  the  dihydro- 
ester,  two  hydrogen  atoms,  and  those  particular  hydrogen  atoms  in 
combination  with  carbon  and  nitrogen  in  the  methenyl-  and  imido- 
groups,  respectively,  will  be  oxidised  off,  and  there  is  formed  a  deriva- 
tive of  pyridine,  containing  no  ring  hydrogen.  While  the  dihydro- 
esters  possess  no  basic  properties,  the  pyridine  derivative  dissolves  in 
acid.  Therefore,  by  treating  the  solution  with  hydrochloric  acid,  it 
can  be  determined  whether  any  unchanged  dihydroester  (insoluble  in 
acid)  is  present. 

Concerning  the  saponification  of  the  ester,  refer  to  what  was  said 
under  Reaction  36. 

The  splitting  off  of  carbon  dioxide  fiom  a  carbonic  acid,  or  a  salt 
of  a  carbonic  acid,  is  generally  designated  as  a  "  pyro-reaction."  For 
this  kind  of  action  a  calcium  salt  is  most  frequently  used ;  this  is  mixed 
with  slaked  lime  and  subjected  to  distillation,  e.g. : 

QH,.|COOca  +  caO|H  =  C6H6  +  CaCO3. 

Calcium  benzoate 

(ca-i  Ca) 

In  poly-basic  acids,  all  the  carboxyl  groups  can  be  replaced  by  hydro- 
gen. In  this  way  an  acid  may  be  transformed  into  the  hydrocarbon 
from  which  it  was  derived.  In  the  above  case,  the  potassium  salt  may 
be  used  instead  of  the  calcium  salt. 


2.    REACTION:    SKRAUP'S  QUINOLINE  SYNTHESIS 
EXAMPLE  :  Quinoline 

In  a  flask  of  about  ii  litres  capacity  containing  a  mixture  of 
24  grammes  of  nitrobenzene,  38  grammes  of  aniline,  and  120 
grammes  of  glycerol,  add,  with  stirring,  100  grammes  of  concen- 
trated sulphuric  acid.  The  flask  is  then  connected  with  a  long, 
wide  reflux  condenser,  and  heated  on  the  sand-bath.  As  soon 


QUINOLINE   SERIES  375 

as  the  reaction  begins,  which  is  recognised  by  the  sudden  evolu- 
tion of  bubbles  of  vapour  ascending  through  the  liquid,  the  flame 
is  removed,  and  the  energetic  reaction  is  allowed  to  complete 
itself  without  further  heating  from  without.  When  the  reaction- 
mixture  has  become  quiet,  it  is  again  heated  for  three  hours  on 
the  sand-bath,  diluted  with  water,  and  from  the  acid  liquid  the 
unchanged  nitrobenzene  is  removed  with  steam.  As  soon  as  no 
drops  of  oil  pass  over,  the  distillation  with  steam  is  discontinued. 
The  liquid  remaining  in  the  distillation  flask  is  allowed  to  cool 
somewhat,  and  then  made  alkaline  with  concentrated  caustic  soda 
solution,  upon  which  the  liberated  quinoline,  mixed  with  the 
unchanged  aniline,  is  distilled  over  with  steam.  Since  these  sub- 
stances cannot  be  separated  by  fractional  distillation,  their  separa- 
tion must  be  effected  by  a  chemical  method.  For  this  purpose 
the  distillate  (oil  and  water  solution)  is  treated  with  dilute  sulphuric 
acid  until  all  oil  is  dissolved  and  an  excess  of  the  acid  is  present ; 
to  the  cold  solution  a  solution  of  sodium  nitrite  is  added  until  a 
drop  of  the  liquid  will  cause  a  blue  spot  on  potassium  iodide-starch 
paper ;  if  the  blue  colour  does  not  appear,  add  more  sulphuric 
acid  to  the  mixture.  The  aniline  (primary  amine)  is  converted 
into  diazobenzenesulphate,  while  the  tertiary  quinoline  remains 
unchanged.  The  mixture  is  heated  for  some  time  on  the  water- 
bath,  by  which,  as  in  Reaction  8,  the  diazo-sulphate  is  converted 
into  phenol.  The  liquid  is  again  made  alkaline,  upon  which  the 
phenol  goes  into  solution,  while  the  quinoline  is  liberated.  The 
mixture  is  now  distilled  with  steam,  and  the  quinoline  is  obtained 
in  a  pure  condition  :  it  is  taken  up  with  ether,  the  ether  evaporated, 
and  the  residue  distilled.  Boiling-point,  237°.  Yield,  40-45 
grammes.  '(See  Wiener  Monatshefte  2,  141.) 

Quinoline  is  formed  in  the  above  reaction  according  to  the  following 
equation : 

H  C.H9.OrI  TT       TT 

HH  \CH.OH  H/\/\H 


+  0=  +4H20 

CH2.CH+         HAH 

H       N 

Quinoline 


376 


SPECIAL   PART 


The  oxygen  necessary  for  the  reaction  is  taken  from  the  nitrobenzene, 
which  is  hereby  reduced  in  a  manner  that  is  not  wholly  clear.  It  is 
possible  that  the  reaction  may  take  place  in  this  way  :  first,  acrolein  is 
formed  from  glycerol,  under  the  influence  of  sulphuric  acid : 


CH2.OH  CH2 
CH.OH  =CH 
OH  CHO 


CH9. 


2H2O, 


Like  all  aldehydes,  this  condenses  with  aniline  to  form  acrolein 
aniline. 

C6H5 .  NH2  +  CHO .  CH=CH2  =  C6H5 .  NzzCH— CH=CH2  +  H2O . 

While  this,  under  the  influence  of  the  oxidising  action  of  the  nitro- 
compound,  loses  two  atoms  of  hydrogen,  and  thus  quinoline  is  formed  : 


Quinoline 

The  Skraup  reaction  is  capable  of  a  very  many-sided  application. 
If,  instead  of  aniline,  its  homologues  are  used,  methyl-,  dimethyl-aniline, 
etc.,  the  corresponding  quinoline  is  obtained.  Also  halogen-,  nitro-, 
etc.,  substituted  amines,  yield  halogen-,  nitro-,  etc.,  substituted  quino- 
lines.  Amidocarbonic  acids,  amidosulphonic  acids,  amidophenols,  yield 
carbonic  acid-,  sulphonic  acid-  or  oxy-derivatives  of  quinoline.  The 
reaction  is  also  applicable  to  the  corresponding  amido-compounds  of 
the  naphthalene  series.  By  starting  from  the  diamines,  two  new  pyri- 
dine  rings,  connected  with  the  benzene  ring,  are  formed ;  in  this  way 
the  so-called  phenanthrolines,  etc.,  are  obtained. 

Of  technical  and  historical  interest  is  the  discovery  which  was  made 
by  Prudhomme  in  the  year  1877,  that  /8-nitroalizarin,  on  heating  with 
glycerol  and  sulphuric  acid,  yields  a  blue  dye,  Alizarin  Blue.  This 
gave  the  impetus  to  Skraup's  synthesis.  To  Grabe's  investigations  we 
are  indebted  for  the  knowledge  of  the  process  by  which,  as  above,  a 
quinoline  synthesis  is  effected  in  the  following  way : 


HYDROCHLORIC  ACID 


377 


OH 


Nitroalizarin 


OH 


Residue  of  the  glycerol  added 
Alizarin  Blue 


IV.    INORGANIC    PART 
1.   CHLORINE 

A  flask  is  one-third  filled  with  manganese  dioxide  (pyrolusite) 
in  pieces  the  size  of  filberts ;  to  this  is  added  a  quantity  of  con- 
centrated hydrochloric  acid  which  is  just  sufficient  to  cover  it. 
On  heating  the  mixture  on  a  wire  gauze  with  a  free  flame,  a  regular 
current  of  chlorine  is  generated ;  this  is  passed  through  two  wash- 
bottles  containing  water  and  concentrated  sulphuric  acid  respect- 
ively ;  the  water  retains  any  hydrochloric  acid  which  is  carried 
along  with  the  gas,  and  the  sulphuric  acid  dries  it.  (See  Figs.  74 
and  87.)  A  piece  of  thin  asbestos-paper  is  placed  on  the  wire 
gauze,  as  is  always  done  on  heating  large  flasks,  by  which  the 
danger  of  breaking  is  essentially  diminished.  A  very  regular 
current  of  chlorine  can  also  be  obtained  from  finely  pulverised 
potassium  dichromate  and  crude  concentrated  hydrochloric  acid 
by  heating  the  mixture  on  the  water-bath.  To  i  litre  of  hydro- 
chloric acid,  use  180-200  grammes  of  pulverised  potassium 
dichromate. 

Concerning  the  preparation  of  chlorine  from  potassium  per- 
manganate and  hydrochloric  acid  see  B.  35,  43. 

2.   HYDROCHLORIC   ACID 

Gaseous  hydrochloric  acid,  which  is  frequently  needed  for  the 
preparation  of  acid-esters,  is  generated  most  conveniently  in  a 


378 


SPECIAL   PART 


Kipp  apparatus  charged  with  fused  ammonium  chloride  in  pieces 
as  large  as  possible,  and  concentrated  sulphuric  acid.  The  opera- 
tion is  conducted  in  the  same  way  as  that  for  the  generation  of 
carbon  dioxide  or  hydrogen  from  a  Kipp  apparatus. 

If  the  apparatus  is  not  available,  the  acid  can  be  generated  very 
conveniently  in  the  following  manner : 

In  concentrated  hydrochloric  acid  contained  in  a  suction  flask 
allow  to  flow  from  a  separating  funnel  concentrated  sulphuric  acid, 
drop  by  drop  (Fig.  82).  The  hydrochloric  acid  evolved  is  dried 
by  passing  it  through  concentrated  sulphuric  acid  contained  in  a 


FIG.  82. 


FIG.  83. 


safety  wash-bottle  (Fig.  83)  ;  this  latter  is  always  used,  since 
otherwise,  with  an  irregular  gas  current,  the  liquid  to  be  saturated 
may  be  easily  drawn  back  into  the  wash-bottle  and  then  into  the 
generating  mixture.  In  place  of  a  Woulff-flask  with  three  tubu- 
lures,  a  single-neck  wash-bottle  may  be  converted  into  a  safety- 
bottle  as  follows  (see  Fig.  84)  :  Into  a  two-hole  cork  place  a 
straight  tube  as  wide  as  possible  ;  through  this  insert  a  narrow 
delivery  tube,  bent  at  a  right  angle,  which  reaches  almost  to  the 
bottom  of  the  bottle. 

The  liquid  to  be  saturated  cannot  flow  back  into  the  wash- 
bottle  with  this  arrangement,  since  in  case  there  should  be  a 
tendency  to  do  so,  air  would  enter  the  suction-flask  through  the 
space  between  the  delivery  tube  and  the  wider  tube,  thus  relieving 


HYDROBROMIC   ACID 


379 


the  pressure.     If  a  wash-bottle  having  a  side-tube  is  available,  it 
can  also  be  converted  into  a  safety-tube  (see  Fig.  85). 


FIG.  84. 


FIG.  85. 


Hydrochloric  acid  gas  may  also  be  obtained  by  warming  10 
parts  of  sodium  chloride  with  a  cold  mixture  of  3  parts  of  water 
and  1 8  parts  of  concentrated  sulphuric  acid. 

3.   HYDROBROMIC   ACID  (see  Brombenzene) 

The  hydrobromic  acid  obtained  as  a  by-product  in  the  bromina- 
tion  reactions  is  purified  by  distilling  it  from  a  fractionating  flask. 
Water  first  passes  over  until  finally  the  temperature  remains  con- 
stant at  126°,  when  a  48  %  acid  goes  over  ;  this  is  collected. 

In  order  to  prepare  potassium  bromide  for  use  in  the  prepara- 
tion of  ethyl  bromide,  the  acid  is  diluted  with  some  water  and 
then  treated  with  dry  potash  until  there  is  no  further  evolution  of 
carbon  dioxide  and  the  liquid  shows  a  neutral  reaction.  To 
i  part  of  hydrobromic  acid  0.5  part  potassium  carbonate  is  used. 
The  water  solution  of  the  potassium  bromide  is  evaporated  to  dry- 
ness  on  a  water-bath.  The  product  thus  obtained  may  be  used 
directly  for  the  preparation  of  ethyl  bromide. 

4.   HYDRIODIC   ACID 

To  44  grammes  of  iodine  (not  pulverised)  contained  in  a  small 
round  flask  of  about  100  c.c.  capacity  (Fig.  86),  gradually  add  4 
grammes  of  yellow  phosphorus  divided  into  about  8  pieces  under 


380  SPECIAL   PART 

water ;  these  are  dried  just  before  transferring  them  to  the  flask,  by 
pressing  between  layers  of  blotting-paper.  The  first  piece  of  phos- 
phorus added  unites  with  the  iodine  with  an  active  evolution  of 
heat  and  light.  When  the  first  action  is  ended,  after  shaking  the 
contents  of  the  flask,  which  soon  become  liquid,  the  second  piece 
is  added.  The  reaction  still  proceeds  with  evident  energy,  al- 
though it  is  less  intense  than  when  the  first  piece  was  added. 
Care  is  taken  to  place  the  phosphorus  as  nearly  as  possible  in  the 
middle  of  the  flask,  and  not  to  allow  it  to  fall  on  the  walls,  since 
otherwise  the  flask  may  be  easily  broken.  When  all  of  the  phos- 
phorus is  added,  a  fused,  dark  mass  of  phosphorus  triiodide  is 
obtained  which  becomes  solid  on  cooling.  The  hydriodic  acid  pre- 
pared from  this  by  warming  with 
water,  must  be  passed  over  red 
phosphorus  in  order  to  free  it 
from  iodine  which  is  carried 
along  with  it.  Proceed  as  fol- 
lows :  5  grammes  of  red  phos- 
phorus are  rubbed  u~?  fo  a  paste 
with  2  c.c.  of  a  water  solution 
of  hydriodic  acid,  or  in  case  this 
is  not  available,  with  as  little 
water  as  possible  (i  c.c.  at  the 
most).  In  this  is  placed  glass 
beads,  or  bits  of  broken  glass, 

which  on  stirring  around  in  the  mixture  become  covered  with  the 
paste.  They  are  then  transferred  to  a  U-tube.  Wide  connecting- 
tubes  are  used  between  the  generating  flask  and  the  U-tube.  In  order 
to  prepare  a  water  solution  of  hydriodic  acid,  the  gas  issuing  from  the 
U-tube  is  passed  into  45  c.c.  of  water  (see  Fig.  86).  The  glass  tube 
is  not  immersed  in  the  water,  but  its  end  must  be  i  cm.  above  the 
surface  ;  otherwise,  in  consequence  of  the  great  affinity  of  water  for 
hydriodic  acid,  under  certain  conditions  the  water  may  be  drawn  back. 
The  hydriodic  acid  is  now  obtained  by  treating  the  completely 
cooled  phosphorus  triiodide  with  6  grammes  of  water  and  warm- 
ing with  a  very  small  luminous  flame.  The  contents  of  the  flask 
steadily  become  clearer,  while  in  the  other  flask  the  heavy  layer 


HYDRIODIC  ACID  381 

of  hydriodic  acid  sinks  to  the  bottom.  The  heating  is  continued 
until  only  a  clear,  colourless  liquid  remains  in  the  generating  flask. 

In  order  to  obtain  a  concentrated  solution  of  hydriodic  acid, 
the  liquid  in  the  receiver  is  distilled.  At  first  a  few  cubic  centi- 
metres of  water  pass  over  at  100°,  then  the  temperature  rises  in 
a  short  time  to  125°;  the  concentrated  acid  passing  over  up  to 
130°  is  collected  separately.  This  boils  for  the  most  part  at  127°. 

This  experiment  teaches  much  concerning  the  chemistry  of 
phosphorus  and  iodine.  First,  it  shows  that  iodine  and  phos- 
phorus unite  directly  with  a  vigorous  reaction,  to  form  phosphorus 

trii'odide  : 

P  +  3I=PI3. 

The  iodide  then  decomposes  with  water,  to  form  hydriodic  acid, 
which  is  evolved,  while  the  phosphorous  acid  (H3PO3)  remains  in 
the  flask  : 

P|i8  +  3H|.OH  =  3  HI  +  PH303. 

The  gaseous  hydriodic  acid  is  an  intensely  fuming  substance, 
which  may  be  easily  shown  by  removing  the  cork  from  the 
receiver  containing  the  aqueous  acid,  for  a  moment.  Hydriodic 
acid  is  absorbed  by  water  with  great  avidity.  The  acid,  boiling 
constantly  at  127°,  contains  approximately  50%  of  anhydrous 
hydriodic  acid. 

In  this  experiment  it  is  observed  that  the  connecting  tubes  of 
the  apparatus,  especially  those  between  the  generating  flask  and 
the  U-tube  become  coated  with  crystals  of  a  diamond-like  bril- 
liancy. These  are  crystals  of  phosphonium  iodide,  PH4I,  which  is 
formed  by  the  decomposition  of  phosphorous  acid. 

It  is  a  common  property  of  all  the  lower  oxidation  products 
of  phosphorus,  to  pass  over  to  the  highest  oxidation  product  — 
phosphoric  acid,  with  the  evolution  of  phosphine  on  heating. 
With  phosphorous  acid,  the  reaction  takes  place  as  follows  : 


The  phosphine  thus  formed  unites,  since  it  possesses  weak  basic 
properties,  with  hydriodic  acid,  to  form  phosphonium  iodide  : 


382  SPECIAL   TART 

Since  this  may  easily  clog  the  connecting  tubes,  the  tubes 
selected  are  as  wide  as  possible.  On  cleaning  the  tubes  with 
water,  this  reacts  with  the  phosphonium  iodide  with  the  evolution 
of  phosphine,  a  gas  with  a  garlic-like  odour,  and  which  in  this 
case  is  not  spontaneously  inflammable.  The  phosphonium  iodide 
decomposes  with  water  into  its  components,  in  accordance  with 
this  equation : 

PH4I  =  PH.,  +  HI. 

This  reaction,  as  is  well  known,  is  employed  for  preparing  pure 
phosphine  which  is  not  spontaneously  inflammable. 

5.  AMMONIA 

Gaseous  ammonia  is  prepared  most  conveniently  by  heating 
the  most  concentrated  ammonia  solution  in  a  flask  over  a  wire 
gauze  with  a  small  flame.  In  order  to  dry  the  gas,  it  is  passed 
through  a  drying  tower  filled  with  soda-lime.  (See  Fig.  66.) 

6.   NITROUS  ACID 

For  the  preparation  of  gaseous  nitrous  acid,  arsenious  acid, 
broken  into  pieces  the  size  of  a  pea,  is  treated  with  nitric  acid, 
sp.  gr.  1.3,  and  heated  gently  on  a  wire  gauze  with  a  free  flame 
(under  the  hood).  In  order  to  condense  the  nitric  acid  carried 
along  with  the  gases,  an  empty  wash-bottle,  cooled  by  cold  water, 
is  employed.  (See  Fig.  81.) 

7.   PHOSPHORUS  TRICHLORIDE 

Under  water,  in  a  porcelain  mortar,  cut  40  grammes  of  yellow 
phosphorus,  with  a  knife  or  chisel,  into  pieces  which  will  con- 
veniently p^iss  into  the  tubulure  of  a  300  c.c.  retort.  After  the  air 
in  the  retort  has  been  displaced  by  dry  carbon  dioxide  (Fig.  87), 
each  single  piece  of  phosphorus  is  taken  from  the  water  by  pincers, 
and  dried  quickly  by  pressing  it  between  several  layers  of  filter- 
paper,  and  immediately  placed  in  the  retort,  care  being  taken  to 
prevent  it  from  becoming  ignited  by  friction  in  the  opening  of 
the  tubulure.  As  soon  as  all  the  phosphorus  has  been  transferred 


PHOSPHORUS  TRICHLORIDE 


383 


to  the  retort,  the  tubulure  is  connected  with  a  delivery  tube  which 
must  move  easily  in  the  cork,  and  a  moderately  rapid  current  of 


dry  chlorine  passed  over  the  phosphorus ;  phosphorus,  chloride  is 
thus  formed  with  evolution  of  heat  and  light.  If  crystals  of  phos- 
phorus pentachloride  should  collect  in  the  neck  of  the  retort,  the 


SPECIAL   PART 


delivery  tube  is  pushed  somewhat  farther  into  the  retort.  If,  on 
the  other  hand,  phosphorus  distils  to  the  upper  part  of  the  retort, 
the  tube  is  somewhat  raised.  The  phosphorus  trichloride  con 
densing  in  the  receiver  is  distilled  from  a  dry  fractionating  flask. 
Boiling-point,  74°.  Yield,  125-140  grammes. 


8.   PHOSPHORUS  OXYCHLORIDEi 

To  100  grammes  of  phosphorus  trichloride,  contained  in  a  large 
tubulated  retort  connected  with  a  condenser,  add  gradually,  in 
small  portions  of  about  2-3  grammes, 
32  grammes  of  finely  pulverised  potas- 
sium chlorate.  After  each  addition, 
wait  until  the  liquid  bubbles  up,  before 
adding  a  new  quantity.  If,  on  the 
addition  of  the  first  portion,  no  reac- 
tion takes  place,  it  is  started  by  a  gentle 
warming.  During  the  addition,  no 
liquid  should  distil  into  the  receiver, 
but  if  this  does  happen,  it  is  poured 
back  into  the  retort.  After  all  of  the 
chlorate  has  been  added,  the  phos- 
phorus oxychloride  formed  is  distilled, 
by  heating  the  retort  in  an  oil-bath, 
to  130°,  or  with  a  luminous  flame.  A 
suction-flask  is  used  as  a  receiver; 
this  is  firmly  connected  with  the  end 
of  the  condenser,  by  means  of  a  cork. 
The  distillate  is  rectified  from  a  frac- 
tionating flask  provided  with  a  thermometer.  Boiling-point,  110°. 
Yield,  loo-no  grammes. 

9.   PHOSPHORUS  PENTACHLORIDE 

Through  the  upper  delivery  tube  of  an  apparatus  similar  to  that 
represented  in  Fig.  88,  a  stream  of  dry  chlorine  is  admitted,  which 


FIG.  88. 


1  J.  pr. 


,  [2]  Vol.  23,382, 


SULPHUROUS   ACID  385 

passes  out  of  the  lower,  right-angled  tube.  From  time  to  time, 
several  cubic  centimetres  of  phosphorus  trichloride  are  allowed  to 
flow  into  the  bottle  from  a  separating  funnel,  upon  which  the 
trichloride  unites  with  the  chlorine  to  form  the  solid  pentachloride. 
Since  this  operation  can  be  repeated,  as  soon  as  it  is  evident  that 
the  union  is  completed,  any  desired  quantity  of  phosphorus  penta- 
chloride can  be  prepared.  Should  the  delivery  tube  become 
stopped  up,  it  is  cleared  by  the  glass  rod  with  which  the  apparatus 
is  provided.  As  the  quantity  of  the  pentachloride  formed  in- 
creases, the  tube  is  correspondingly  raised.  Yield,  quantitative. 

10.   SULPHUROUS  ACID 

Gaseous  sulphurous  acid  is  generated  in  an  apparatus  similar  to 
the  one  represented  in  Fig.  82,  by  adding  to  a  concentrated  water 
solution  of  sodium  hydrogen  sulphite  a  cold  mixture  of  equal  parts, 
by  volume,  of  water  and  concentrated  sulphuric  acid,  drop  by  drop. 
The  generating  flask  i?  shaken  frequently,  to  keep  the  contents 
from  separating  into  layers. 

11.   SODIUM 

(a)  To  cut  Sodium.  —  In  order  to  divide  sodium  into  small 
portions,  it  can  be  cut  into  scales  with  a  knife,  or  pressed  out  into 
a  wire  with  a  sodium-press.  To  cut  it  into  scales,  an  apparatus 
similar  to  that  represented  in  Fig.  89  is  convenient.  After  both 

sides  of  the  knife  and  the  front  part 
of  the  table  have  been  coated  with 
a  thin  layer  of  vaseline,  a  long  stick 
of  the  metal  to  be  cut,  the  end  of 
which  is  wrapped  in  filter-paper,  in 
order    that    it    may   be    handled,  is 
>\    placed  on  the  table  so  that  it  projects 
somewhat  over  the  front  end ;   it  is 
FlG-  89'  then  cut  with  a  short  stroke  of  the 

knife.     On  the  front  part  of  the  lower  platform  is  placed  a  small 
dish  filled  with  ether  or  ligroi'n,  into  which  the  scales  fall.     When 
2  c 


386  SPECIAL   PART 

using  the  knife,  two  points  are  to  be  especially  observed.  The 
eye  is  never  placed  in  front  of  the  knife,  but  always  behind  it,  so 
that  the  fingers  holding  the  sodium  can  always  be  seen.  Only  in 
this  way  can  a  wound  be  prevented.  Further,  the  cross-section 
of  the  piece  of  sodium  must  not  be  too  large,  otherwise  the  metal 
adheres  to  the  knife.  Quadratic  scales,  the  edge  of  which  must 
not,  at  most,  be  more  than  5-6  mm.  long,  are  cut.  With  a  little 
practice,  large  quantities  of  the  metal  can  be  cut  in  very  thin 
scales  in  a  short  time. 

The  sodium  residues  are  not  thrown  into  water  nor  into  waste- 
jars,  but  are  dropped  into  alcohol  contained  in  a  beaker  or  flask. 

(b)  Sodium  Amalgam.  —  Sodium  scales,  about  the  size  of  a 
20-cent  piece,  are  pressed  to  the  bottom  of  mercury  contained  in 
a  porcelain  mortar,  in  rather  rapid  succession,  by  means  of  a  short, 
moderately  thick  glass  rod,  drawn  out  to  a  point  and  bent  at  a 
short  right  angle.  The  scales  are  speared  on  the  glass  rod  (under 
the  hood ;  eyes  protected  by  spectacles  ;  hands,  with  gloves) . 

The  mercury  may  also  be  warmed  in  a  porcelain  casserole  on 
the  water-bath  (60-70°),  and,  without  further  heating,  small 
pieces  of  sodium,  the  size  of  a  half  bean,  are  thrust  to  the  bottom 
of  the  vessel  with  the  aid  of  a  glass  rod. 

12.    ALUMINIUM  CHLORIDE 

A  wide  tube,  diameter  1^—2  cm.,  of  hard  glass  drawn  out  to 
a  narrow  tube,  is  at  one  end  connected  by  means  of  a  cork 
with  a  wide-neck  so-called  "salt  bottle"  (Fig.  90).  The  cork 
with  which  this  is  closed  is  supplied  with  a  second,  smaller  hole, 
bearing  a  delivery  tube  of  at  least  9  mm.  diameter,  extending 
to  the  centre  of  the  receiver.  The  tube  is  half  filled  (half  of 
its  cross-section)  with  aluminium  shavings,  which  have  been 
previously  freed  from  oil  by  boiling  with  alcohol  and  then  dried 
in  an  air-bath  at  120°;  an  asbestos  plug  is  placed  at  each  end 
of  the  layer.  A  rapid  current  of  hydrochloric  acid  gas,  most 
conveniently  obtained  from  a  Kipp  apparatus  charged  with  fused 
ammonium  chloride  and  concentrated  sulphuric  acid,  is  passed 


ALUMINIUM   CHLORIDE  387 

through  the  apparatus.  Care  must  be  taken  that  the  drying  flask 
containing  sulphuric  acid  is  not  too  small,  since  the  acid  foams 
easily.  As  soon  as  the  air  is  driven  out  of  the  apparatus,  —  this 
has  been  accomplished  when  the  gas.  evolved  is  completely 
absorbed  by  water  (a  piece  of  rubber  tubing  is  attached  to  the 
tube,  and  the  gas  tested  from  time  to  time  by  immersing  the  end 
of  the  tubing  in  water  in  a  beaker),  —  the  tube  is  heated  in  a  com- 
bustion furnace  throughout  its  entire  length,  at  first  with  small 
flames,  which  are  gradually  increased  (Fig.  90).  When  the  flames 
have  reached  a  certain  size,  white  vapours  of  aluminium  chloride, 
condensing  in  the  receiver,  are  noticed.  The  reaction  is  ended 
as  soon  as  the  aluminium,  except  for  a  small,  dark-coloured  resi- 


ITTTmTTl 


FIG.  90. 

due,  disappears.  For  the  success  of  the  preparation,  the  following 
points  are  particularly  observed  :  ( i )  All  parts  of  the  apparatus 
must  be  perfectly  dry.  (2)  The  air  must  be  removed  as  com- 
pletely as  possible,  since,  otherwise,  an  explosion  of  oxygen  and 
hydrogen  may  take  place.  (3)  The  portion  of  the  tube  extend- 
ing beyond  the  furnace  must  be  as  short  as  possible,  to  prevent 
the  aluminium  chloride  from  condensing  in  it,  which  results  in  a 
stopping  up  of  the  apparatus.  In  order  that  the  cork  may  not 
burn,  it  is  protected  by  an  asbestos  plate,  provided  with  a  circular 
hole  in  the  centre.  (4)  The  aluminium  must  not  be  heated  to 
melting.  If  this  should  happen  at  any  particular  point,  the  flames 
must  be  immediately  lowered.  (5)  The  hydrochloric  acid  cur- 
rent must  be  extremely  rapid.  One  should  not  be  able  to  count 
single  bubbles  of  the  gas,  but  they  should  follow  one  another 


388  SPECIAL  PART 

uninterruptedly.  The  evolution  of  a  small  quantity  of  a  smoky 
vapour  from  the  outlet-tube  will  always  occur,  but  the  greatest 
part  of  the  aluminium  chloride  is  condensed  even  if  the  hydro- 
chloric acid  rushes  through  the  wash-bottles.  Should  the  first 
experiment  be  unsuccessful,  in  consequence  of  a  stoppage  of  the 
tube,  the  method  for  correcting  this  will  readily  suggest  itself. 

Recently  it  has  been  shown  that  it  is  better  to  use  for  the  re- 
ceiver an  iron  tube  25  cm.  long  and  4  cm.  wide  (inner  diameter). 
To  one  end  of  this  is  welded  a  narrower  tube,  2  cm.  long;  by 
filing  it  on  the  inside  the  end  is  given  a  somewhat  conical  shape ; 
it. is  selected  of  such  a  diameter  that  the  glass  tube  can  fae  fastened 
in  it  with  a  few  turns  of  asbestos  paper.  The  end  not  narrowed 
is  closed  by  a  cork  bearing  a  glass  tube  as  wide  as  possible  lead- 
ing to  the  hood.  A  receiver  of  this  kind  is  advantageous  because 
the  glass  tube  can  be  heated  strongly  to  its  extreme  end,  and  thus 
a  stopping  up  of  the  apparatus  may  be  entirely  prevented.  If  the 
iron  tube  should  become  too  hot,  a  wet  towel  is  placed  on  it  and 
moistened  from  time  to  time. 

The  aluminium  chloride  condensing  in  the  receiver  is  preserved 
in  well-closed  bottles,  or  best,  in  a  desiccator. 

13.    LEAD  PEROXIDE 

In  a  large  porcelain  dish  dissolve,  with  heat,  50  grammes  of 
lead  acetate  in  250  c.c.  of  water,  and  treat  with  a  solution  of 
bleaching-powder,  prepared  by  shaking  TOO  grammes  of  bleaching- 
powder  with  T^-  litres  of  water  and  filtering,  heat  not  quite  to 
boiling,  until  the  precipitate,  bright  at  first,  becomes  deep  dark 
brown.  A  small  test-portion  is  then  filtered  hot,  and  the  filtrate 
treated  with  the  bleaching-powder  solution  and  heated  to  boiling ; 
if  a  dark  brown  precipitate  is  formed,  more  of  the  bleaching- 
powder  solution  is  added  to  the  main  quantity,  and  it  is  heated 
until  a  test  gives  no  precipitate  with  the  bleaching-powder  solution. 
The  main  quantity  of  the  liquid  is  separated  from  the  heavy  pre- 
cipitate by  decantation ;  the  latter  is  washed  several  times  with 
water  (decantation),  and  then  filtered  with  suction;  the  precipi- 


LEAD   PEROXIDE  389 

tate  is  washed  repeatedly  with  water.  The  lead  peroxide  is  not 
dried,  but  is  preserved  in  a  closed  vessel  in  the  form  of  a  thick 
paste. 

Value  Determination,  —  In  order  to  determine  the  value  of  the 
paste,  a  weighed  portion  is  heated  with  hydrochloric  acid,  the 
chlorine  evolved  is  passed  into  a  solution  of  potassium  iodide, 

N 

and  the  liberated  iodine  is  titrated  with  a  —  solution  of  sodium 

10 

thiosulphate  (refer  to  a  text-book  on  Volumetric  Analysis) .  The 
determination,  carried  out  as  follows,  is  sufficiently  accurate  for 
preparation  work  :  On  an  analytical  balance  weigh  off  exactly  6.2 
grammes  of  pure,  crystallised  sodium  thiosulphate ;  this  is  dis- 
solved in  enough  cold  water  to  make  the  volume  of  the  solution 
just  250  c.c.  In  a  small  flask  weigh  off  0.5-1  gramme  of  the 
peroxide  paste ;  treat  this  (with  cooling)  with  a  mixture  of  equal 
volumes  of  concentrated  hydrochloric  acid  and  water ;  the  flask 
is  immediately  connected  with  a  delivery  tube,  and  this  is  inserted 
in  an  inverted  retort,  the  neck  of  which  has  been  expanded  to  a 
bulb,  and  which  contains  a  solution  of  four  grammes  of  potassium 
iodide  in  water.  When  heat  is  applied  to  the  flask,  chlorine  is 
generated,  which  liberates  iodine  from  the  potassium  iodide. 
After  the  end  of  the  heating,  care  is  taken  that  the  potassium 
iodide  solution  is  not  drawn  back  into  the  flask.  The  contents 
of  the  retort  are  then  poured  into  a  beaker  and  treated  with  the 
thiosulphate  solution  from  a  burette  until  the  yellow  colour  of 
the  iodine  just  disappears.  Since  a  molecule  of  the  peroxide 
liberates  two  atoms  of  iodine,  a  cubic  centimetre  of  the  thiosul- 
phate solution  corresponds  to  — —  =  .012  gramme  pure  lead 
peroxide. 

14.  CUPROUS  CHLORIDE 

Heat  a  solution  of  50  grammes  of  copper  sulphate  and  24 
grammes  of  salt  to  60-70°.  Into  this  conduct  a  current  of  sulphur 
dioxide  until  the  precipitate  of  cuprous  chloride  no  longer  increases. 
The  precipitate  is  filtered  with  suction  and  washed,  first  with  sul- 


3QO  SPECIAL   PART 

phurous  acid  and  then  with  glacial  acetic  acid  until  it  runs  through 
colourless.  The  moist  preparation  is  then  heated  in  a  shallow 
porcelain  dish  or  a  large  watch  crystal  on  the  water- bath  until  the 
odour  of  acetic  acid  cannot  be  detected.  It  is  preserved  in  a  well- 
closed  flask. 

15.   DETERMINATION   OF   THE  VALUE  OF   ZINC  DUST 

From  a  weighing-tube  pour  into  a  100  c.c.  round  flask  o.i 
gramme  zinc  dust  (exact  weighing)  and  add  a  few  cubic  centi- 
metres of  water.  The  flask  is  closed  by  a  good  three- hole  cork. 
In  the  middle  one  is  inserted  a  small  dropping  funnel ;  the  side 
holes  carry  the  inlet  and  outlet  tubes  (Fig.  91).  The  stem  of 
the  funnel  is  previously  filled  with  water  by  open- 
ing the  cock,  immersing  the  end  in  water  and 
applying  suction.  The  inlet  tube  is  connected  with 
a  Kipp  carbon  dioxide  generator,  and  the  outlet 
tube  with  a  nitrometer  charged  with  a  solution  of 
caustic  potash.  Carbon  dioxide  is  passed  into  the 
apparatus  until  all  the  gas  escaping  from  the  outlet 
tube  is  absorbed  by  the  potash.  The  current  of 
carbon  dioxide  is  then  lessened  and  from  the  drop- 
ping funnel  a  mixture  of  10  c.c.  of  concentrated 
FIG.  91.  hydrochloric  acid  and  10  c.c.  water  containing  a 
few  drops  of  platinic  chloride,  is  allowed  to  flow  in  on  the  zinc 
dust ;  the  flask  is  finally  heated.  From  the  volume  of  hydrogen 
obtained  the  percentage  of  zinc  in  the  zinc  dust  may  be  calcu- 
lated. The  individual  operations  of  this  analysis  are  conducted 
as  described  under  "  Determination  of  Nitrogen." 


INDEX 


Abbreviations,  395. 
Acetacetic  ester,  179. 
Acetaldehyde,  167. 
Acetamide,  151. 
Acetanilide,  145. 
Acetic  anhydride,  147. 
Acetic  ester,  157. 
Acetonitrile,  155. 
Acetyl  chloride,  141. 
Active  mandelic  acid,  309. 
Aldehyde,  167. 
Aldehyde-ammonia,  169. 
Alizarin,  367. 
Aluminium  chloride,  386. 
Amidoazobenzene,  265. 
Amidodimethyl  aniline,  258. 
Ammonia,  382. 
Ammonium  eosin,  360. 
Aniline,  215. 
Animal  charcoal,  50. 
Anthracene,  369. 
Anthraquinone,  370. 
Antipyrine,  255. 
Autoclaves,  68. 
Azines,  303. 
Azobenzene,.  226. 
Azo  dyes,  256. 
Azoxybenzene,  226. 

Beckmann's  Reaction,  320. 
Benzal  chloride,  298. 
Benzaldehyde,  298. 
Benzamide,  318. 
Benzene  from  aniline  237. 
Benzene  from  phenylhydrazine,  250. 
Benzenesulphinic  acid,  287. 
Benzenesulphon  amide,  280. 


Benzenesulphon  chloride,  280. 

Benzenesulphonic  acid,  280. 

Benzhydrol,  348. 

Benzidine,  231. 

Benzil,  306. 

Ben  zoic  acid,  299,  303,  348. 

Benzoi'cphenylester,  318. 

Benzoin,  304. 

Benzophenone,  320. 

Benzophenone  oxime,  320. 

Benzotrichloride,  300. 

Benzoyl  chloride,  317. 

Benzyl  alcohol,  303. 

Benzyl  chloride,  300. 

Bitter  almond  green,  356. 

Boiling-point,  corrections  of,  32. 

Bomb-furnace,  66. 

Bomb-tubes,  63. 

Brombenzene,  271. 

Bromethane,  131. 

Bromine  carrier,  273. 

Bromine,  determination  of,  80,  128. 

Briihl's  apparatus,  15,  27. 

Biichner  funnel,  58. 

"  Bumping,"  31. 

Butlerow's  Synthesis,  146. 

Butyric  acid,  185. 

Carbon,  determination  of,  101. 
Carbon  monoxide,  332. 
Chloracetic  acid,  163. 
Chlorine,  377. 

Chlorine,  determination  of,  80,  128. 
Cinnamic  acid,  313. 
Cleaning  the  hands,  76. 
Cleaning  vessels,  75. 
Collidine,  371. 
391 


392 


INDEX 


Collidinedicarbonic  ester,  372. 
Congo-paper,  258. 
Crystallisation,  i. 
Crystal  violet,  364. 
Cuprous  chloride,  389. 

Decolourising,  50. 
Diazoamidobenzene,  262. 
Diazobenzeneimide,  239. 
Diazobenzeneperbromide,  238. 
Diazo-compounds,  237. 
Diazonium  compounds,  238. 
Diazotisation,  237. 
Dibrombenzene,  271. 
Dihydrocollidinedicarbonic  ester,  371. 
Dimethylcyclohexenone,  203. 
Dinitrobenzene,  212. 
Diphenyliodonium  iodide,  244. 
Diphenylmethane,  329. 
Diphenylthiourea,  234. 
Disazo  dyes,  261. 
Distillation,  16. 
Distillation  with  steam,  37. 
Distribution  coefficient,  46. 
Drying,  52. 
Drying  agents,  53. 
Drying,  of  vessels,  75. 

Elementary     Analysis,      Dennstedt's 

Method,  113. 
Eosin,  357. 
Ether,  pure,  277,  348. 
Ethyl  acetate,  157. 
Ethyl  benzene,  276. 
Ethyl  bromide,  131. 
Ethylidene  bisacetacetic  ester,  202. 
Ethylene,  191. 
Ethylene  alcohol,  196. 
Ethylene  bromide,  191. 
Ethyl  iodide,  133. 
Ethyl  malonic  acid,  187. 
Ethyl  malonic  ester,  185. 
Extraction  with  ether,  44. 

Filter  press,  59. 
Filtration,  56. 
Fittig's  Synthesis,  276. 


Fluorescei'n,  357. 
Fractional  crystallisation,  n. 
.Fractional  distillation,  23. 
Friedel-Crafts'  Reaction,  320. 
Fuchsine-paper,  258. 

Gattermann-Koch  Reaction,  331. 
Glycol,  196. 
Glycoldiacetate,  196. 
Grignard's  Reaction,  348. 
Guanidine,  234. 

Halogens,  determinations  of,  80,  128. 
Heating  under  pressure,  63. 
Helianthine,  256. 
Hofmann  Reaction,  176. 
Hydrazobenzene,  226. 
Hydrazones,  254. 
Hydriodic  acid,  379. 
Hydrobromic  acid,  379. 
Hydrochloric  acid,  377. 
Hydrocinnamic  acid,  316. 
Hydrogen,  determination  of,  101,  113. 
Hydroquinone,  270. 

Inactive  mandelic  acid,  307. 
Iodine  chloride,  165. 
Iodine,  determination  of,  80,  128. 
lodobenzene,  244. 
lodoethane,  133. 
lodosobenzene,  244. 
Isodiazo  compounds,  239. 
Isonitrile  reaction,  222. 

Knoevenagel's  ring  closing,  202. 
Kolbe's  Reaction,  344. 

Law  of  Mass  Action,  159. 
Lead  peroxide,  388. 

Malachite  green,  354. 

Malonic  ester,  185. 

Mandelic  acid,  307. 

Mandelic  nitrile,  307. 

Melting-point,  determination  of,  71. 

Methyl  amine,  175. 

Methylene  blue,  262. 


INDEX 


393 


Michler's  ketone,  364. 
Monobrombenzene,  271. 
Monochloracetic  acid,  163. 

Naphthalenesulphonic  acid  (/3)(  290. 

Naphthol  (18),  293. 

Nitroaniline,  215. 

Nitrobenzene,  212. 

Nitrogen,  determination  of,  90,  124. 

Nitrophenol  (o  and  p) ,  296. 

Nitroso  benzene,  223. 

Nitrous  acid,  382. 

Opening  bomb  tubes,  66. 
Osazones,  254. 
Oxybenzaldehyde  (p),  341. 

Perkin's  Reaction,  313. 
Phenol  from  aniline,  243. 
Phenyldisulphide,  290. 
Phenylhydrazine,  250. 
Phenylhydroxylamine,  223. 
Phenyliodide,  244. 
Phenyliodide  chloride,  244. 
Phenyliodite,  244. 
Phenyl  magnesium  bromide,  350. 
Phenyl  magnesium  iodide,  348. 
Phenyl  mercaptan,  289. 
Phenyl  mustard  oil,  233. 
Phosphorus  oxychloride,  384. 
Phosphorus  pentachloride,  384. 
Phosphorus  trichloride,  382. 
Pipette,  capillary,  43. 
Potassium  acetate,  197. 
Potassium  collidine  dicarbonate,  372. 
Potassium-iodide-starch-paper,  241. 
Pressure  flasks,  68. 
Pukall  cells,  59. 
Pyro-reaction,  374; 

Qualitative  tests  for  carbon,  hydrogen, 

nitrogen,  sulphur,  chlorine,  bromine, 

iodine,  77. 
Quantitative    determination    of   carbon 

and  hydrogen,  101,  113. 
Quantitative  determination  of  halogens, 

80,  128. 


Quantitative  determination  of  nitrogen, 

90,  124. 
Quantitative   determination  of  sulphur, 

86,  125,  127. 
Quinizarin,  365. 
Quinoline,  374. 
Quinone,  266. 

Reduction  of  an  azo  dye,  256. 
Runge's  Reaction,  221. 

Safety  wash-bottle,  378. 

Salicylic  acid,  344. 

Salicylic  aldehyde,  340. 

'  Salting  out,'  49. 

Sandmeyer's  Reaction,  249. 

Saponification  of  ethyl   malonic   ester, 

187. 

Schotten-Baumann  Reaction,  318. 
Sealing  of  bomb-tubes,  63. 
Separation  by  extraction,  theory  of,  46. 
Separation  of  liquids,  43. 
Sodium,  385. 

Sodium  acetate,  anhydrous,  147. 
Sodium  amalgam,  386. 
Sodium  eosin,  360. 
Sodium  knife,  385. 
Solubility  product,  287. 
Solvents,  2. 
Steam  distillation,  37. 
Sublimation,  14. 
Sulphanilic  acid,  235. 
Sulphobenzide,  280. 
Sulphur,  determination  of,  86,  125,  127. 
Sulphurous  acid,  385. 
Superheated  steam,  41. 

Tarry  matter,  removal  of,  50. 
Terephthalic  acid,  337. 
Testing  thermometers,  74. 
Tests  for  carbon,  77. 
Tests  for  halogen,  79.  . 
Tests  for  hydrogen,  77. 
Tests  for  nitrogen,  77. 
Tests  for  sulphur,  78. 
Thermometer,  tests  of,  74. 
Thiocarbanilide,  232. 


394 


INDEX 


Thiophenol,  287. 
Toluic  acid,  335. 
Tolyl  aldehyde,  331. 
Tolyl  nitrile,  248. 
Trimethylpyridine,  371. 
Triphenylguanidine,  233. 


Vacuum  distillation,  25. 
Volhard  Tubes,  68. 

Xylenol  (s),  204. 

Zinc  dust  determination,  390. 
Zinc  dust  distillation,  369. 


ABBREVIATIONS 


A.        =  Liebig's  Annalen  der  Chemie. 

A.  ch.  =  Annales  de  chimie  et  de  physique. 

B.  =  Berliner  Berichte. 

Bl.       =  Bulletin  de  la  societe  chimique  de  Paris. 

Ch-Z.  =  Chemiker  Zeitung. 

J.         =  Jahresbericht  liber  die  Fortschritte  der  Chemie. 

J.  pr.  =  Journal  fur  praktische  Chemie. 

P.        =  Poggendorff' s  Annalen. 

R.        =  Journal  der  russischen  chemischen  Gesellschaft 

Z.        =  Zeitschrift  fur  Chemie. 


395 


396 


TABLE  FOR  NITROGEN   DETERMINATION 


00    w      co<<tOOONrO"3-OOrt 
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M      O        t"1    OO        IH    SO        IH      ^f      >H      CO      M      M 


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TABLE  FOR  NITROGEN  DETERMINATION 


397 


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398 


TABLE   FOR  NITROGEN   DETERMINATION 


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TABLE  FOR  NITROGEN   DETERMINATION 


399 


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t        §          ~ 


400 


TABLE   FOR  NITROGEN   DETERMINATION 


o    oso 


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